diff --git a/CHANGELOG.md b/CHANGELOG.md
index 53e4d8e..e440538 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,10 @@
+## 1.0.0
+
+* _Tested with dart `2.13`._
+* Refactored to support for null safety.
+* Updated SDK constraints to `>=2.12.0 <3.0.0` for null safety.
+* Switch to using `package:lints`.
+
 ## 0.2.1
 
 * _Minor pub updates and tested with dart `2.10`._
diff --git a/README.md b/README.md
index 1b2d851..95b38ee 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@
 [![Build Status](https://travis-ci.com/raycardillo/dart_phonetics.svg?branch=master)](https://travis-ci.com/raycardillo/dart_phonetics)
 [![Pub package](https://img.shields.io/pub/v/dart_phonetics)](https://pub.dev/packages/dart_phonetics)
 [![Dartdoc reference](https://img.shields.io/badge/dartdoc-reference-blue)](https://pub.dev/documentation/dart_phonetics/latest/)
+[![style: lint](https://img.shields.io/badge/style-lint-4BC0F5.svg)](https://pub.dev/packages/lint)
 [![Project license](https://img.shields.io/badge/license-Apache%202.0-informational)](https://www.apache.org/licenses/LICENSE-2.0)
 
 A collection of phonetic algorithms for [Dart](https://dart.dev/) and [Flutter](https://flutter.dev/). These algorithms help find words or names that sound similar by generating an encoding that can be compared or indexed for fuzzy searching.
diff --git a/analysis_options.yaml b/analysis_options.yaml
index 108d105..117cfbe 100644
--- a/analysis_options.yaml
+++ b/analysis_options.yaml
@@ -1 +1,6 @@
-include: package:pedantic/analysis_options.yaml
+include: package:lints/recommended.yaml
+
+linter:
+  rules:
+    constant_identifier_names: false
+    non_constant_identifier_names: false
\ No newline at end of file
diff --git a/example/main.dart b/example/main.dart
index 93b76b3..069a4ee 100644
--- a/example/main.dart
+++ b/example/main.dart
@@ -3,7 +3,7 @@ import 'package:dart_phonetics/dart_phonetics.dart';
 void _printResult(PhoneticEncoder encoder, String input) {
   final encoding = encoder.encode(input);
   print(
-      '${encoder?.runtimeType?.toString()} - "$input"\n  primary = ${encoding?.primary}\n  alternate = ${encoding?.alternates}\n');
+      '${encoder.runtimeType.toString()} - "$input"\n  primary = ${encoding?.primary}\n  alternate = ${encoding?.alternates}\n');
 }
 
 void main() {
@@ -13,7 +13,7 @@ void main() {
   _printResult(soundex, inputString);
 
   final customSoundex = Soundex.fromMapping(Soundex.americanMapping,
-      maxLength: null, paddingEnabled: false, ignoreHW: false);
+      maxLength: 0, paddingEnabled: false, ignoreHW: false);
   _printResult(customSoundex, inputString);
 
   final refinedSoundex = RefinedSoundex.defaultEncoder;
@@ -22,8 +22,7 @@ void main() {
   final nysiisOriginal = Nysiis.originalEncoder;
   _printResult(nysiisOriginal, inputString);
 
-  final nysiisModified =
-      Nysiis.withOptions(maxLength: null, enableModified: true);
+  final nysiisModified = Nysiis.withOptions(maxLength: 0, enableModified: true);
   _printResult(nysiisModified, inputString);
 
   final doubleMetaphone = DoubleMetaphone.withMaxLength(12);
diff --git a/lib/src/double_metaphone.dart b/lib/src/double_metaphone.dart
index 7f8e616..f429f11 100644
--- a/lib/src/double_metaphone.dart
+++ b/lib/src/double_metaphone.dart
@@ -29,22 +29,22 @@ class _DoubleMetaphoneEncoding {
   /// Buffer used for writing alternate encoding.
   final StringBuffer _alternate = StringBuffer();
 
-  /// Max length to encode (or `null` if no max length).
+  /// Max length to encode (defaults to `0` for no max length).
   final int _maxLength;
 
   /// Internal constructor.
-  _DoubleMetaphoneEncoding([this._maxLength]);
+  _DoubleMetaphoneEncoding([this._maxLength = 0]);
 
   /// Append a [charCode] to the primary encoding.
   void appendPrimary(final int charCode) {
-    if (_maxLength == null || _primary.length < _maxLength) {
+    if (_maxLength <= 0 || _primary.length < _maxLength) {
       _primary.writeCharCode(charCode);
     }
   }
 
   /// Append a [charCode] to the alternate encoding.
   void appendAlternate(final int charCode) {
-    if (_maxLength == null || _alternate.length < _maxLength) {
+    if (_maxLength <= 0 || _alternate.length < _maxLength) {
       _alternate.writeCharCode(charCode);
     }
   }
@@ -97,11 +97,10 @@ class _DoubleMetaphoneEncoding {
   }
 
   /// Returns `true` if the encoding is maxed out (both encodings are at the
-  /// max length), `false` otherwise (or if [_maxLength] is `null`).
+  /// max length), `false` otherwise (or if [_maxLength] is `0`).
   bool isMaxedOut() {
-    return _maxLength != null &&
-        _primary.length >= _maxLength &&
-        _alternate.length >= _maxLength;
+    return _maxLength > 0 && _primary.length >= _maxLength && _alternate
+        .length >= _maxLength;
   }
 
   /// Returns the string value of the primary encoding. This renders the
@@ -142,7 +141,7 @@ class DoubleMetaphone implements PhoneticEncoder {
   /// Default metaphone encoding length to use.
   static const int defaultMaxLength = 4;
 
-  /// Maximum length of the encoding, where `null` indicates no maximum.
+  /// Maximum length of the encoding, where `0` indicates no maximum.
   final int maxLength;
 
   // Set.contains() for single character matches are fast and convenient
@@ -246,13 +245,18 @@ class DoubleMetaphone implements PhoneticEncoder {
 
   //#endregion
 
+  /// Encodes a string using the Double Metaphone algorithm as configured.
+  ///
   /// Per specification, the encoding always contains two values. If there is
   /// no alternate, the primary and the alternate encodings will be the same.
+  ///
+  /// Returns a [PhoneticEncoding] for the [input] String or
+  /// `null` if the [input] is empty (after cleaning up).
   @override
-  PhoneticEncoding encode(String input) {
+  PhoneticEncoding? encode(String input) {
     // clean up the input and convert to uppercase
     input = PhoneticUtils.clean(input);
-    if (input == null) {
+    if (input.isEmpty) {
       return null;
     }
 
@@ -368,7 +372,7 @@ class DoubleMetaphone implements PhoneticEncoder {
 
     final primary = encoding.primary;
     final alternate = encoding.alternate;
-    return PhoneticEncoding(primary, (alternate.isEmpty ? null : {alternate}));
+    return PhoneticEncoding(primary, {alternate});
   }
 
   //#region Special Encoding Rules
diff --git a/lib/src/encoder.dart b/lib/src/encoder.dart
index 1c28fc6..ff03730 100644
--- a/lib/src/encoder.dart
+++ b/lib/src/encoder.dart
@@ -20,14 +20,14 @@
 /// phonetically encoding an input string.
 class PhoneticEncoderException implements Exception {
   /// The input that was being processed when the exception occurred.
-  /// This should only be `null` if the input being encoded was `null`.
+  /// This may be empty if the input being encoded was empty after cleanup.
   final String input;
 
   /// A message describing the problem that was encountered.
   final String message;
 
   /// Optionally indicates another exception that was the root cause.
-  final Exception cause;
+  final Exception? cause;
 
   /// Creates a new PhoneticEncoderException with an optional root [cause].
   PhoneticEncoderException(this.input, this.message, [this.cause]);
@@ -49,7 +49,7 @@ class PhoneticEncoding {
   final String primary;
 
   /// An alternative phonetic encoding for algorithms that support this.
-  final Set<String> alternates;
+  final Set<String>? alternates;
 
   /// Creates an instance of this data class.
   PhoneticEncoding(this.primary, [this.alternates]);
@@ -63,6 +63,6 @@ class PhoneticEncoding {
 
 /// The common interface for all phonetic encoders.
 abstract class PhoneticEncoder {
-  /// Returns a [PhoneticEncoding] for the [input] String.
-  PhoneticEncoding encode(String input);
+  /// Returns a [PhoneticEncoding] for the [input] String or `null`.
+  PhoneticEncoding? encode(String input);
 }
diff --git a/lib/src/nysiis.dart b/lib/src/nysiis.dart
index c20c6cf..318ec7c 100644
--- a/lib/src/nysiis.dart
+++ b/lib/src/nysiis.dart
@@ -56,7 +56,7 @@ class Nysiis implements PhoneticEncoder {
   /// Default encoding length to use for the modified algorithm.
   static const int defaultModifiedMaxLength = 8;
 
-  /// Maximum length of the encoding, where `null` indicates no maximum.
+  /// Maximum length of the encoding, where `0` indicates no maximum.
   final int maxLength;
 
   /// Indicates if the "modified" rules should be applied when encoding.
@@ -276,9 +276,7 @@ class Nysiis implements PhoneticEncoder {
     // NOTE: per specification, this loop starts at the second character.
     for (var i = 1; i < chars.length; i++) {
       final char = chars[i];
-      if (char == null) {
-        break;
-      } else if (PhoneticUtils.isSpecialCharacter(char)) {
+      if (PhoneticUtils.isSpecialCharacter(char)) {
         continue;
       }
 
@@ -401,11 +399,14 @@ class Nysiis implements PhoneticEncoder {
 
   /// Encodes a string using the NYSIIS algorithm as configured. This encoder
   /// does not produce any [PhoneticEncoding.alternates] values.
+  ///
+  /// Returns a [PhoneticEncoding] for the [input] String or
+  /// `null` if the [input] is empty (after cleaning up).
   @override
-  PhoneticEncoding encode(String input) {
+  PhoneticEncoding? encode(String input) {
     // clean up the input and convert to uppercase
     input = PhoneticUtils.clean(input);
-    if (input == null) {
+    if (input.isEmpty) {
       return null;
     }
 
@@ -430,7 +431,7 @@ class Nysiis implements PhoneticEncoder {
 
     // truncate the encoding to maxLength if required
     var finalEncoding = String.fromCharCodes(encoding);
-    if (maxLength != null && finalEncoding.length > maxLength) {
+    if (maxLength > 0 && finalEncoding.length > maxLength) {
       finalEncoding = finalEncoding.substring(0, maxLength);
     }
 
diff --git a/lib/src/refined_soundex.dart b/lib/src/refined_soundex.dart
index 1eb3c24..bd6b522 100644
--- a/lib/src/refined_soundex.dart
+++ b/lib/src/refined_soundex.dart
@@ -36,7 +36,7 @@ class RefinedSoundex implements PhoneticEncoder {
   /// ignore the input character and do not encode it (e.g., vowels).
   final Map<int, int> soundexMapping;
 
-  /// Maximum length of the encoding (and how much to pad if [paddingEnabled]).
+  /// Maximum length of the encoding, where `0` indicates no maximum.
   final int maxLength;
 
   /// This is a default mapping of the 26 letters used in US English.
@@ -81,7 +81,7 @@ class RefinedSoundex implements PhoneticEncoder {
   /// Creates a custom Soundex instance. This constructor can be used to
   /// provide custom mappings for non-Western character sets, etc.
   factory RefinedSoundex.fromMapping(final Map<int, int> soundexMapping,
-          {int maxLength}) =>
+          {int maxLength = 0}) =>
       RefinedSoundex._internal(Map.unmodifiable(soundexMapping), maxLength);
 
   /// Gets the [defaultEncoder] instance of a RefinedSoundex encoder.
@@ -89,13 +89,15 @@ class RefinedSoundex implements PhoneticEncoder {
 
   //#endregion
 
-  /// Returns a [PhoneticEncoding] for the [input] String.
-  /// Returns `null` if the input is `null` or empty (after cleaning up).
+  /// Encodes a string using the Refined Soundex algorithm as configured.
+  ///
+  /// Returns a [PhoneticEncoding] for the [input] String or
+  /// `null` if the [input] is empty (after cleaning up).
   @override
-  PhoneticEncoding encode(String input) {
+  PhoneticEncoding? encode(String input) {
     // clean up the input and convert to uppercase
     input = PhoneticUtils.clean(input, allowLatin: false);
-    if (input == null) {
+    if (input.isEmpty) {
       return null;
     }
 
@@ -105,7 +107,7 @@ class RefinedSoundex implements PhoneticEncoder {
     // always write first character
     soundex.writeCharCode(input.codeUnitAt(0));
 
-    int last, current;
+    int? last, current;
     last = $asterisk;
 
     // encode all characters
@@ -117,7 +119,7 @@ class RefinedSoundex implements PhoneticEncoder {
         soundex.writeCharCode(current);
       }
 
-      if (maxLength != null && soundex.length >= maxLength) {
+      if (maxLength > 0 && soundex.length >= maxLength) {
         break;
       }
 
diff --git a/lib/src/soundex.dart b/lib/src/soundex.dart
index 34ce92c..4ac3f84 100644
--- a/lib/src/soundex.dart
+++ b/lib/src/soundex.dart
@@ -85,7 +85,8 @@ class Soundex implements PhoneticEncoder {
   /// The character to use for padding (when [paddingEnabled] is `true`).
   final int paddingChar;
 
-  /// Maximum length of the encoding (and how much to pad if [paddingEnabled]).
+  /// Maximum length of the encoding, where `0` indicates no maximum,
+  /// and how much to pad if [paddingEnabled].
   final int maxLength;
 
   /// This is a default mapping of the 26 letters used in US English.
@@ -186,13 +187,13 @@ class Soundex implements PhoneticEncoder {
     return input.split(RegExp(r'\s*-\s*'));
   }
 
-  /// Returns a single encoding for the [input] String.
-  /// Returns `null` if the input is `null` or empty (after cleaning up).
+  /// Returns a [PhoneticEncoding] for the [input] String or
+  /// an empty string if the [input] is empty (after cleaning up).
   String _encode(String input) {
     // clean up the input and convert to uppercase
     input = PhoneticUtils.clean(input, allowLatin: false);
-    if (input == null) {
-      return null;
+    if (input.isEmpty) {
+      return input;
     }
 
     // we'll write to a buffer to avoid string copies
@@ -228,13 +229,13 @@ class Soundex implements PhoneticEncoder {
         }
       }
 
-      if (maxLength != null && soundex.length >= maxLength) {
+      if (maxLength > 0 && soundex.length >= maxLength) {
         break;
       }
     }
 
     // pad the encoding if required
-    if (paddingEnabled && maxLength != null) {
+    if (paddingEnabled && maxLength > 0) {
       while (soundex.length < maxLength) {
         soundex.writeCharCode(paddingChar);
       }
@@ -252,11 +253,15 @@ class Soundex implements PhoneticEncoder {
     }
   }
 
-  /// Returns a [PhoneticEncoding] for the [input] String.
-  /// Returns `null` if the input is `null` or empty (after cleaning up).
+  /// Encodes a string using the Soundex algorithm as configured.
+  ///
+  /// Returns a [PhoneticEncoding] for the [input] String or
+  /// `null` if the [input] is empty (after cleaning up).
   @override
-  PhoneticEncoding encode(String input) {
-    if (input == null || input.isEmpty) {
+  PhoneticEncoding? encode(String input) {
+    // clean up the input and convert to uppercase
+    input = PhoneticUtils.clean(input, allowLatin: false);
+    if (input.isEmpty) {
       return null;
     }
 
@@ -285,17 +290,15 @@ class Soundex implements PhoneticEncoder {
     // now go through all parts and add more alternates
     while (iterator.moveNext()) {
       final part = iterator.current;
-      if (part != null) {
-        alternates.add(_encode(part));
-        if (prefixesEnabled) {
-          _addTrimmedPrefixToAlternates(alternates, part);
-        }
+      alternates.add(_encode(part));
+      if (prefixesEnabled) {
+        _addTrimmedPrefixToAlternates(alternates, part);
       }
     }
 
     // remove the primary if it made it into the alternate list from others
     alternates.remove(primary);
 
-    return PhoneticEncoding(primary, alternates.isEmpty ? null : alternates);
+    return PhoneticEncoding(primary, alternates);
   }
 }
diff --git a/lib/src/utils.dart b/lib/src/utils.dart
index 07b16d8..993c4fd 100644
--- a/lib/src/utils.dart
+++ b/lib/src/utils.dart
@@ -125,8 +125,8 @@ class PhoneticUtils {
   /// need to do additional cleaning if you're working with strings
   /// that are particularly dirty.
   static String clean(final String value, {bool allowLatin = true}) {
-    if (value == null || value.isEmpty) {
-      return null;
+    if (value.isEmpty) {
+      return value;
     }
 
     final cleaned = value
@@ -136,7 +136,7 @@ class PhoneticUtils {
         .replaceAll(
             (allowLatin) ? _cleanLatinAllowed : _cleanLatinNotAllowed, '');
 
-    return cleaned.isEmpty ? null : cleaned;
+    return cleaned;
   }
 
   /// Returns the character from [value] at [index] or [$nul] if the index is
@@ -186,7 +186,7 @@ class PhoneticUtils {
   ///
   /// Despite the name, this is actually a measure of similarity.
   /// This naming is consistent with the SQL `DIFFERENCE` function definition.
-  static int differenceEncoded(final String e1, final String e2) {
+  static int differenceEncoded(final String? e1, final String? e2) {
     if (e1 == null || e1.isEmpty || e2 == null || e2.isEmpty) {
       return 0;
     }
diff --git a/misc/experiments/single_char_exp.dart b/misc/experiments/single_char_exp.dart
index 0d8bf07..40423c3 100644
--- a/misc/experiments/single_char_exp.dart
+++ b/misc/experiments/single_char_exp.dart
@@ -30,9 +30,8 @@ void main() {
   final watch = Stopwatch();
 
   const numIterations = 2000000;
-  var vowelsFound;
+  var vowelsFound = 0;
 
-  vowelsFound = 0;
   print('running if statement matching...');
   watch.start();
   for (var i = 0; i < numIterations; i++) {
diff --git a/pubspec.lock b/pubspec.lock
index 90513b6..2597f43 100644
--- a/pubspec.lock
+++ b/pubspec.lock
@@ -7,342 +7,342 @@ packages:
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "11.0.0"
+    version: "22.0.0"
   analyzer:
     dependency: transitive
     description:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.40.4"
+    version: "1.7.0"
   args:
     dependency: transitive
     description:
       name: args
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.6.0"
+    version: "2.1.1"
   async:
     dependency: transitive
     description:
       name: async
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.4.2"
+    version: "2.7.0"
   boolean_selector:
     dependency: transitive
     description:
       name: boolean_selector
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   charcode:
     dependency: "direct main"
     description:
       name: charcode
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.3"
+    version: "1.3.1"
   cli_util:
     dependency: transitive
     description:
       name: cli_util
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.0"
+    version: "0.3.0"
   collection:
     dependency: transitive
     description:
       name: collection
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.14.13"
+    version: "1.15.0"
   convert:
     dependency: transitive
     description:
       name: convert
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.1"
+    version: "3.0.0"
   coverage:
     dependency: transitive
     description:
       name: coverage
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.14.1"
+    version: "1.0.3"
   crypto:
     dependency: transitive
     description:
       name: crypto
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.5"
-  glob:
+    version: "3.0.1"
+  file:
     dependency: transitive
     description:
-      name: glob
+      name: file
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0"
-  http:
+    version: "6.1.2"
+  frontend_server_client:
     dependency: transitive
     description:
-      name: http
+      name: frontend_server_client
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.2"
+    version: "2.1.0"
+  glob:
+    dependency: transitive
+    description:
+      name: glob
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.0.1"
   http_multi_server:
     dependency: transitive
     description:
       name: http_multi_server
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.2.0"
+    version: "3.0.1"
   http_parser:
     dependency: transitive
     description:
       name: http_parser
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "3.1.4"
+    version: "4.0.0"
   io:
     dependency: transitive
     description:
       name: io
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.4"
+    version: "1.0.0"
   js:
     dependency: transitive
     description:
       name: js
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.6.2"
+    version: "0.6.3"
+  lints:
+    dependency: "direct dev"
+    description:
+      name: lints
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "1.0.1"
   logging:
     dependency: transitive
     description:
       name: logging
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.11.4"
+    version: "1.0.1"
   matcher:
     dependency: transitive
     description:
       name: matcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.9"
+    version: "0.12.10"
   meta:
     dependency: transitive
     description:
       name: meta
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.3"
+    version: "1.4.0"
   mime:
     dependency: transitive
     description:
       name: mime
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.7"
-  node_interop:
-    dependency: transitive
-    description:
-      name: node_interop
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.1.1"
-  node_io:
-    dependency: transitive
-    description:
-      name: node_io
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.1.1"
+    version: "1.0.0"
   node_preamble:
     dependency: transitive
     description:
       name: node_preamble
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.12"
+    version: "2.0.1"
   package_config:
     dependency: transitive
     description:
       name: package_config
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.3"
+    version: "2.0.0"
   path:
     dependency: transitive
     description:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.0"
   pedantic:
-    dependency: "direct dev"
+    dependency: transitive
     description:
       name: pedantic
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.2"
+    version: "1.11.1"
   pool:
     dependency: transitive
     description:
       name: pool
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.0"
+    version: "1.5.0"
   pub_semver:
     dependency: transitive
     description:
       name: pub_semver
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.4"
+    version: "2.0.0"
   shelf:
     dependency: transitive
     description:
       name: shelf
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.9"
+    version: "1.1.4"
   shelf_packages_handler:
     dependency: transitive
     description:
       name: shelf_packages_handler
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "3.0.0"
   shelf_static:
     dependency: transitive
     description:
       name: shelf_static
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.8"
+    version: "1.0.0"
   shelf_web_socket:
     dependency: transitive
     description:
       name: shelf_web_socket
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.3"
+    version: "1.0.1"
   source_map_stack_trace:
     dependency: transitive
     description:
       name: source_map_stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   source_maps:
     dependency: transitive
     description:
       name: source_maps
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.10.9"
+    version: "0.10.10"
   source_span:
     dependency: transitive
     description:
       name: source_span
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.7.0"
+    version: "1.8.1"
   stack_trace:
     dependency: transitive
     description:
       name: stack_trace
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.9.5"
+    version: "1.10.0"
   stream_channel:
     dependency: transitive
     description:
       name: stream_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.0"
+    version: "2.1.0"
   string_scanner:
     dependency: transitive
     description:
       name: string_scanner
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.5"
+    version: "1.1.0"
   term_glyph:
     dependency: transitive
     description:
       name: term_glyph
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "1.2.0"
   test:
     dependency: "direct dev"
     description:
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.15.4"
+    version: "1.17.8"
   test_api:
     dependency: transitive
     description:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.2.18"
+    version: "0.4.1"
   test_core:
     dependency: transitive
     description:
       name: test_core
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.11+1"
+    version: "0.3.28"
   typed_data:
     dependency: transitive
     description:
       name: typed_data
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.2.0"
+    version: "1.3.0"
   vm_service:
     dependency: transitive
     description:
       name: vm_service
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.2.0"
+    version: "7.1.0"
   watcher:
     dependency: transitive
     description:
       name: watcher
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.9.7+15"
+    version: "1.0.0"
   web_socket_channel:
     dependency: transitive
     description:
       name: web_socket_channel
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.1.0"
+    version: "2.1.0"
   webkit_inspection_protocol:
     dependency: transitive
     description:
       name: webkit_inspection_protocol
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.7.3"
+    version: "1.0.0"
   yaml:
     dependency: transitive
     description:
       name: yaml
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.2.1"
+    version: "3.1.0"
 sdks:
-  dart: ">=2.7.0 <3.0.0"
+  dart: ">=2.12.0 <3.0.0"
diff --git a/pubspec.yaml b/pubspec.yaml
index 548a6b9..4094c52 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,15 +1,15 @@
 name: dart_phonetics
 description: A collection of phonetic algorithms. These algorithms help find words or names that sound similar by generating an encoding that can be compared or indexed for fuzzy searching.
-version: 0.2.1
+version: 1.0.0
 homepage: https://github.com/raycardillo/dart_phonetics
 repository: https://github.com/raycardillo/dart_phonetics
 
 environment:
-  sdk: ">=2.2.2 <3.0.0"
+  sdk: ">=2.12.0 <3.0.0"
 
 dependencies:
-  charcode: ^1.1.3
+  charcode: ^1.3.1
 
 dev_dependencies:
-  test: ^1.15.4
-  pedantic: ^1.9.2
+  test: ^1.17.8
+  lints: ^1.0.1
diff --git a/test/double_metaphone_test.dart b/test/double_metaphone_test.dart
index 5155cd3..32e5657 100644
--- a/test/double_metaphone_test.dart
+++ b/test/double_metaphone_test.dart
@@ -56,7 +56,7 @@ void main() {
     // https://scholar.google.com/scholar?cluster=634245576371390488&hl=en&as_sdt=0,21&as_vis=1
     test('test performance paper examples', () {
       final encoder = DoubleMetaphone.defaultEncoder;
-      final encoderNoMax = DoubleMetaphone.withMaxLength(null);
+      final encoderNoMax = DoubleMetaphone.withMaxLength(0);
 
       //expectEncoding(encoder, 'Phonetic', 'FNTK');
       expectEncoding(encoderNoMax, 'Phonetic', 'FNTK');
diff --git a/test/nysiis_test.dart b/test/nysiis_test.dart
index 3c7a2be..517ebad 100644
--- a/test/nysiis_test.dart
+++ b/test/nysiis_test.dart
@@ -49,7 +49,7 @@ void main() {
       expectEncoding(encoder8, 'PFEISTER', 'FASTAR');
       expectEncoding(encoder8, 'SCHOENHOEFT', 'SANAFT');
 
-      final encoderNoMax = Nysiis.withOptions(maxLength: null);
+      final encoderNoMax = Nysiis.withOptions(maxLength: 0);
       expectEncoding(encoderNoMax, 'PHILLIPSON', 'FALAPSAN');
       expectEncoding(encoderNoMax, 'PFEISTER', 'FASTAR');
       expectEncoding(encoderNoMax, 'SCHOENHOEFT', 'SANAFT');
@@ -60,7 +60,7 @@ void main() {
     // https://scholar.google.com/scholar?cluster=634245576371390488&hl=en&as_sdt=0,21&as_vis=1
     test('test performance paper examples', () {
       final encoder = Nysiis.originalEncoder;
-      final encoderNoMax = Nysiis.withOptions(maxLength: null);
+      final encoderNoMax = Nysiis.withOptions(maxLength: 0);
 
       expectEncoding(encoder, 'Phonetic', 'FANATA');
       expectEncoding(encoderNoMax, 'Phonetic', 'FANATAC');
@@ -75,7 +75,7 @@ void main() {
     // version the "modified" implementation is not the same as the USDA
     // version of the modified algorithm that is implemented here.
     test('test original dropby.com examples', () {
-      final encoder = Nysiis.withOptions(maxLength: null);
+      final encoder = Nysiis.withOptions(maxLength: 0);
       expectEncoding(encoder, 'MACINTOSH', 'MCANT');
       expectEncoding(encoder, 'KNUTH', 'NAT');
       expectEncoding(encoder, 'KOEHN', 'CAN');
@@ -117,7 +117,7 @@ void main() {
 
     // http://ntz-develop.blogspot.com/2011/03/phonetic-algorithms.html
     test('test ntz examples', () {
-      final encoder = Nysiis.withOptions(maxLength: null);
+      final encoder = Nysiis.withOptions(maxLength: 0);
       expectEncoding(encoder, 'Diggell', 'DAGAL');
       expectEncoding(encoder, 'Dougal', 'DAGAL');
       expectEncoding(encoder, 'Doughill', 'DAGAL');
@@ -281,7 +281,7 @@ void main() {
       expectEncoding(encoder8, 'SCHOENHOEFT', 'SANAFT');
 
       final encoderNoMax =
-          Nysiis.withOptions(maxLength: null, enableModified: true);
+          Nysiis.withOptions(maxLength: 0, enableModified: true);
       expectEncoding(encoderNoMax, 'PHILLIPSON', 'FALAPSAN');
       expectEncoding(encoderNoMax, 'PFEISTER', 'FASTAR');
       expectEncoding(encoderNoMax, 'SCHOENHOEFT', 'SANAFT');
@@ -293,7 +293,7 @@ void main() {
     // version the "modified" implementation is not the same as the USDA
     // version of the modified algorithm that is implemented here.
     test('test modified dropby.com examples', () {
-      final encoder = Nysiis.withOptions(maxLength: null, enableModified: true);
+      final encoder = Nysiis.withOptions(maxLength: 0, enableModified: true);
       expectEncoding(encoder, 'MACINTOSH', 'MCANTAS');
       expectEncoding(encoder, 'KNUTH', 'NAT');
       expectEncoding(encoder, 'KOEHN', 'CAN');
diff --git a/test/refined_soundex_test.dart b/test/refined_soundex_test.dart
index 5c98721..b4ecb56 100644
--- a/test/refined_soundex_test.dart
+++ b/test/refined_soundex_test.dart
@@ -88,7 +88,7 @@ void main() {
       // test some strings with irregular characters
       expectEncoding(encoder, '#@', null);
       expectEncoding(encoder, '<test&ing>', 'T6036084');
-      expectEncoding(encoder, '\0#tes@ting!', 'T6036084');
+      expectEncoding(encoder, '${$nul}#tes@ting!', 'T6036084');
       expectEncoding(encoder, ' \t\n\r Washington \t\n\r ', 'W03084608');
     });
 
@@ -130,9 +130,7 @@ void main() {
       // testing examples from:
       // http://ntz-develop.blogspot.com/2011/03/phonetic-algorithms.html
 
-      var inputs;
-
-      inputs = [
+      var inputs = [
         'Braz',
         'Broz',
       ];
@@ -196,7 +194,6 @@ void main() {
       final encoder = RefinedSoundex();
 
       // Edge cases
-      expect(0, PhoneticUtils.primaryDifference(encoder, null, null));
       expect(0, PhoneticUtils.primaryDifference(encoder, '', ''));
       expect(0, PhoneticUtils.primaryDifference(encoder, ' ', ' '));
 
diff --git a/test/smoke_test.dart b/test/smoke_test.dart
index 8771461..0b3c686 100644
--- a/test/smoke_test.dart
+++ b/test/smoke_test.dart
@@ -25,8 +25,7 @@ import 'test_utils.dart';
 void main() {
   group('Utility Smoke Tests', () {
     test('null behavior', () {
-      expect(PhoneticUtils.clean(null), null);
-      expect(PhoneticUtils.clean(''), null);
+      expect(PhoneticUtils.clean(''), '');
       expect(PhoneticUtils.differenceEncoded(null, ''), 0);
       expect(PhoneticUtils.differenceEncoded('', null), 0);
     });
diff --git a/test/soundex_test.dart b/test/soundex_test.dart
index 2ba99d6..0b69e85 100644
--- a/test/soundex_test.dart
+++ b/test/soundex_test.dart
@@ -90,7 +90,7 @@ void main() {
       expectEncoding(encoder10, 'supercalifragilistic', 'S162416242');
 
       final encoderNoMax =
-          Soundex.fromMapping(Soundex.americanMapping, maxLength: null);
+          Soundex.fromMapping(Soundex.americanMapping, maxLength: 0);
       expectEncoding(encoderNoMax, 'testing', 'T2352');
       expectEncoding(encoderNoMax, 'supercalifragilistic', 'S16241624232');
     });
@@ -100,7 +100,7 @@ void main() {
 
       expectEncoding(encoder, '#@', null);
       expectEncoding(encoder, '<test&ing>', 'T235');
-      expectEncoding(encoder, '\0#tes@ting!', 'T235');
+      expectEncoding(encoder, '${$nul}#tes@ting!', 'T235');
       expectEncoding(encoder, ' \t\n\r Washington \t\n\r ', 'W252');
     });
 
@@ -110,7 +110,7 @@ void main() {
     test('test performance paper examples', () {
       final encoder = Soundex();
       final encoderNoMax =
-          Soundex.fromMapping(Soundex.americanMapping, maxLength: null);
+          Soundex.fromMapping(Soundex.americanMapping, maxLength: 0);
 
       expectEncoding(encoder, 'Phonetic', 'P532');
       expectEncoding(encoderNoMax, 'Phonetic', 'P532');
@@ -387,9 +387,7 @@ void main() {
 
       expectEncoding(encoder, 'Fusedale', 'F234');
 
-      var inputs;
-
-      inputs = [
+      var inputs = [
         'Genthner',
         'Gentner',
         'Gianettini',
@@ -617,7 +615,6 @@ void main() {
       final encoder = Soundex();
 
       // Edge cases
-      expect(0, PhoneticUtils.primaryDifference(encoder, null, null));
       expect(0, PhoneticUtils.primaryDifference(encoder, '', ''));
       expect(0, PhoneticUtils.primaryDifference(encoder, ' ', ' '));
 
diff --git a/test/test_utils.dart b/test/test_utils.dart
index 5dbb683..0ef9d2e 100644
--- a/test/test_utils.dart
+++ b/test/test_utils.dart
@@ -23,13 +23,15 @@ import 'package:test/test.dart';
 void expectEncodingEquals(
     PhoneticEncoder encoder, String input1, String input2) {
   final encoding1 = encoder.encode(input1);
+  final encoding1Alternates = encoding1?.alternates;
   final encoding2 = encoder.encode(input2);
+  final encoding2Alternates = encoding2?.alternates;
 
   final foundMatch = ((encoding1?.primary == encoding2?.primary) ||
-      (encoding1?.alternates != null &&
-          encoding1.alternates.contains(encoding2?.primary)) ||
-      (encoding2?.alternates != null &&
-          encoding2.alternates.contains(encoding1?.primary)));
+      (encoding1Alternates != null &&
+          encoding1Alternates.contains(encoding2?.primary)) ||
+      (encoding2Alternates != null &&
+          encoding2Alternates.contains(encoding1?.primary)));
 
   expect(true, foundMatch,
       reason: 'Match not found between '
@@ -38,8 +40,8 @@ void expectEncodingEquals(
 
 /// Verify an encoding matches [expected] for a single [input].
 void expectEncoding(
-    PhoneticEncoder encoder, String input, String expectedPrimary,
-    [List<String> expectedAlternates]) {
+    PhoneticEncoder encoder, String input, String? expectedPrimary,
+    [List<String>? expectedAlternates]) {
   final encoding = encoder.encode(input);
   expect(encoding?.primary, expectedPrimary,
       reason: 'Primary failed for input=$input');
@@ -51,9 +53,9 @@ void expectEncoding(
 
 /// Verify an encoding matches [expected] for a list of [inputs].
 void expectEncodings(
-    PhoneticEncoder encoder, List<String> inputs, String expectedPrimary,
-    [List<String> expectedAlternates]) {
-  inputs.forEach((input) {
+    PhoneticEncoder encoder, List<String> inputs, String? expectedPrimary,
+    [List<String>? expectedAlternates]) {
+  for (var input in inputs) {
     expectEncoding(encoder, input, expectedPrimary, expectedAlternates);
-  });
+  }
 }