diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.cs
index 9314e23ef311e..57e46ec6dcac2 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.cs
@@ -8,7 +8,7 @@ namespace Microsoft.Extensions.Configuration
 {
     public static partial class FileConfigurationExtensions
     {
-        public static System.Action<Microsoft.Extensions.Configuration.FileLoadExceptionContext> GetFileLoadExceptionHandler(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
+        public static System.Action<Microsoft.Extensions.Configuration.FileLoadExceptionContext>? GetFileLoadExceptionHandler(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
         public static Microsoft.Extensions.FileProviders.IFileProvider GetFileProvider(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder SetBasePath(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, string basePath) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder SetFileLoadExceptionHandler(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<Microsoft.Extensions.Configuration.FileLoadExceptionContext> handler) { throw null; }
@@ -27,10 +27,11 @@ public override void Load() { }
     public abstract partial class FileConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         protected FileConfigurationSource() { }
-        public Microsoft.Extensions.FileProviders.IFileProvider FileProvider { get { throw null; } set { } }
-        public System.Action<Microsoft.Extensions.Configuration.FileLoadExceptionContext> OnLoadException { get { throw null; } set { } }
+        public Microsoft.Extensions.FileProviders.IFileProvider? FileProvider { get { throw null; } set { } }
+        public System.Action<Microsoft.Extensions.Configuration.FileLoadExceptionContext>? OnLoadException { get { throw null; } set { } }
         public bool Optional { get { throw null; } set { } }
-        public string Path { get { throw null; } set { } }
+        [System.Diagnostics.CodeAnalysis.DisallowNull]
+        public string? Path { get { throw null; } set { } }
         public int ReloadDelay { get { throw null; } set { } }
         public bool ReloadOnChange { get { throw null; } set { } }
         public abstract Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder);
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
index f7a69d4e76c85..2e8aa6b1a125f 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/ref/Microsoft.Extensions.Configuration.FileExtensions.csproj
@@ -1,6 +1,8 @@
 <Project Sdk="Microsoft.NET.Sdk">
+
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationExtensions.cs
index 4ce12bd020caf..815905130036a 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationExtensions.cs
@@ -43,9 +43,9 @@ public static IFileProvider GetFileProvider(this IConfigurationBuilder builder)
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            if (builder.Properties.TryGetValue(FileProviderKey, out object provider))
+            if (builder.Properties.TryGetValue(FileProviderKey, out object? provider))
             {
-                return provider as IFileProvider;
+                return (IFileProvider)provider;
             }
 
             return new PhysicalFileProvider(AppContext.BaseDirectory ?? string.Empty);
@@ -94,14 +94,14 @@ public static IConfigurationBuilder SetFileLoadExceptionHandler(this IConfigurat
         /// </summary>
         /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
-        public static Action<FileLoadExceptionContext> GetFileLoadExceptionHandler(this IConfigurationBuilder builder)
+        public static Action<FileLoadExceptionContext>? GetFileLoadExceptionHandler(this IConfigurationBuilder builder)
         {
             if (builder == null)
             {
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            if (builder.Properties.TryGetValue(FileLoadExceptionHandlerKey, out object handler))
+            if (builder.Properties.TryGetValue(FileLoadExceptionHandlerKey, out object? handler))
             {
                 return handler as Action<FileLoadExceptionContext>;
             }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationProvider.cs
index aef7acc13e5e9..60811023f6b38 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationProvider.cs
@@ -17,7 +17,7 @@ namespace Microsoft.Extensions.Configuration
     /// </summary>
     public abstract class FileConfigurationProvider : ConfigurationProvider, IDisposable
     {
-        private readonly IDisposable _changeTokenRegistration;
+        private readonly IDisposable? _changeTokenRegistration;
 
         /// <summary>
         /// Initializes a new instance with the specified source.
@@ -30,7 +30,7 @@ public FileConfigurationProvider(FileConfigurationSource source)
             if (Source.ReloadOnChange && Source.FileProvider != null)
             {
                 _changeTokenRegistration = ChangeToken.OnChange(
-                    () => Source.FileProvider.Watch(Source.Path),
+                    () => Source.FileProvider.Watch(Source.Path!),
                     () =>
                     {
                         Thread.Sleep(Source.ReloadDelay);
@@ -53,12 +53,12 @@ public override string ToString()
 
         private void Load(bool reload)
         {
-            IFileInfo file = Source.FileProvider?.GetFileInfo(Source.Path);
+            IFileInfo? file = Source.FileProvider?.GetFileInfo(Source.Path ?? string.Empty);
             if (file == null || !file.Exists)
             {
                 if (Source.Optional || reload) // Always optional on reload
                 {
-                    Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+                    Data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
                 }
                 else
                 {
@@ -100,7 +100,7 @@ static Stream OpenRead(IFileInfo fileInfo)
                 {
                     if (reload)
                     {
-                        Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+                        Data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
                     }
                     var exception = new InvalidDataException(SR.Format(SR.Error_FailedToLoad, file.PhysicalPath), ex);
                     HandleException(ExceptionDispatchInfo.Capture(exception));
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationSource.cs
index 1122e6f171553..d58c265f406a9 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileConfigurationSource.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using Microsoft.Extensions.FileProviders;
 
@@ -15,12 +16,13 @@ public abstract class FileConfigurationSource : IConfigurationSource
         /// <summary>
         /// Used to access the contents of the file.
         /// </summary>
-        public IFileProvider FileProvider { get; set; }
+        public IFileProvider? FileProvider { get; set; }
 
         /// <summary>
         /// The path to the file.
         /// </summary>
-        public string Path { get; set; }
+        [DisallowNull]
+        public string? Path { get; set; }
 
         /// <summary>
         /// Determines if loading the file is optional.
@@ -41,7 +43,7 @@ public abstract class FileConfigurationSource : IConfigurationSource
         /// <summary>
         /// Will be called if an uncaught exception occurs in FileConfigurationProvider.Load.
         /// </summary>
-        public Action<FileLoadExceptionContext> OnLoadException { get; set; }
+        public Action<FileLoadExceptionContext>? OnLoadException { get; set; }
 
         /// <summary>
         /// Builds the <see cref="IConfigurationProvider"/> for this source.
@@ -56,8 +58,8 @@ public abstract class FileConfigurationSource : IConfigurationSource
         /// <param name="builder">The <see cref="IConfigurationBuilder"/>.</param>
         public void EnsureDefaults(IConfigurationBuilder builder)
         {
-            FileProvider = FileProvider ?? builder.GetFileProvider();
-            OnLoadException = OnLoadException ?? builder.GetFileLoadExceptionHandler();
+            FileProvider ??= builder.GetFileProvider();
+            OnLoadException ??= builder.GetFileLoadExceptionHandler();
         }
 
         /// <summary>
@@ -70,8 +72,8 @@ public void ResolveFileProvider()
                 !string.IsNullOrEmpty(Path) &&
                 System.IO.Path.IsPathRooted(Path))
             {
-                string directory = System.IO.Path.GetDirectoryName(Path);
-                string pathToFile = System.IO.Path.GetFileName(Path);
+                string? directory = System.IO.Path.GetDirectoryName(Path);
+                string? pathToFile = System.IO.Path.GetFileName(Path);
                 while (!string.IsNullOrEmpty(directory) && !Directory.Exists(directory))
                 {
                     pathToFile = System.IO.Path.Combine(System.IO.Path.GetFileName(directory), pathToFile);
@@ -84,6 +86,5 @@ public void ResolveFileProvider()
                 }
             }
         }
-
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileLoadExceptionContext.cs b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileLoadExceptionContext.cs
index a87c82339f58c..1d619335d5e88 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileLoadExceptionContext.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/FileLoadExceptionContext.cs
@@ -13,12 +13,12 @@ public class FileLoadExceptionContext
         /// <summary>
         /// The <see cref="FileConfigurationProvider"/> that caused the exception.
         /// </summary>
-        public FileConfigurationProvider Provider { get; set; }
+        public FileConfigurationProvider Provider { get; set; } = null!;
 
         /// <summary>
         /// The exception that occurred in Load.
         /// </summary>
-        public Exception Exception { get; set; }
+        public Exception Exception { get; set; } = null!;
 
         /// <summary>
         /// If true, the exception will not be rethrown.
diff --git a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
index c256903f01cc2..e2c041ade1833 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.FileExtensions/src/Microsoft.Extensions.Configuration.FileExtensions.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
     <!-- Use targeting pack references instead of granular ones in the project file. -->
     <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>