build: Enable nullable reference types

Enable nullable reference types by default but disable for demo and test data projects.
Disable nullable for all code files where errors were found

src/Directory.Build.props

@@ -1,7 +1,8 @@
 <Project>
 
   <PropertyGroup>
-    <LangVersion>7.3</LangVersion>
+    <LangVersion>8.0</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <PropertyGroup>

src/MdDocs.ApiReference.DemoProject/Grynwald.MdDocs.ApiReference.DemoProject.csproj

@@ -8,6 +8,7 @@
     <IsPackable>false</IsPackable>
     <AssemblyVersion>1.2.3</AssemblyVersion>
     <Version>1.2.3</Version>
+    <Nullable>disable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/MdDocs.ApiReference.Model.Test/TestBase.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Linq;
 using System.Reflection;
 using Grynwald.MdDocs.ApiReference.Model;

src/MdDocs.ApiReference.Model.Test/XmlDocs/XmlDocsProviderTest.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.IO;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model;

src/MdDocs.ApiReference.Model.Test/XmlDocs/_Ids/MemberIdLexerTest.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Reflection;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;

src/MdDocs.ApiReference.Model.Test/XmlDocs/_Ids/MemberIdParserTest.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableEventId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;
 

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableFieldId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;
 

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableMemberId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;
 

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableMethodId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableNamespaceId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;
 

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializablePropertyId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;

src/MdDocs.ApiReference.Model.Test/_Helpers/XunitSerializableTypeId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model;
 using Xunit.Abstractions;

src/MdDocs.ApiReference.Model/EventDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 using Mono.Cecil;
 

src/MdDocs.ApiReference.Model/FieldDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 using Mono.Cecil;
 

src/MdDocs.ApiReference.Model/IndexerOverloadDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;

src/MdDocs.ApiReference.Model/MethodLikeOverloadDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;

src/MdDocs.ApiReference.Model/ModuleDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;

src/MdDocs.ApiReference.Model/ParameterDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 using Grynwald.Utilities.Collections;
 using Mono.Cecil;

src/MdDocs.ApiReference.Model/PropertyDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 using Grynwald.Utilities.Collections;

src/MdDocs.ApiReference.Model/TypeDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;

src/MdDocs.ApiReference.Model/TypeParameterDocumentation.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 using Grynwald.Utilities.Collections;
 using Mono.Cecil;

src/MdDocs.ApiReference.Model/XmlDocs/NullXmlDocsProvider.cs

@@ -1,4 +1,6 @@
-namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
+#nullable disable
+
+namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {
     /// <summary>
     /// Empty implementation of <see cref="IXmlDocsProvider"/>.

src/MdDocs.ApiReference.Model/XmlDocs/SeeAlsoElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/XmlDocsReader.cs

@@ -1,4 +1,6 @@
-// The code in this file is derived from the "DocReader" class from the NuDoq project.
+#nullable disable
+
+// The code in this file is derived from the "DocReader" class from the NuDoq project.
 // The original version of this file was downloaded from
 // https://github.com/kzu/NuDoq/blob/56ad8c508003490d859214753591440b123616f5/src/NuDoq/DocReader.cs
 //

src/MdDocs.ApiReference.Model/XmlDocs/_Ids/MemberIdParser.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 

src/MdDocs.ApiReference.Model/XmlDocs/_Ids/TypeIdBuilder.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/CElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/CodeElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/ListElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/ListItemElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/ParaElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/ParamRefElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/SeeElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/TextBlock.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/TextElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/XmlDocs/_TextElements/TypeParamRefElement.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model.XmlDocs
 {

src/MdDocs.ApiReference.Model/_Extensions/CustomAttributeProviderExtensions.cs

@@ -1,4 +1,6 @@
-using System.Linq;
+#nullable disable
+
+using System.Linq;
 using Mono.Cecil;
 
 namespace Grynwald.MdDocs.ApiReference.Model

src/MdDocs.ApiReference.Model/_Extensions/MethodReferenceExtensions.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Linq;
 using Mono.Cecil;
 

src/MdDocs.ApiReference.Model/_Extensions/XElementExtensions.cs

@@ -1,4 +1,6 @@
-using System.Xml.Linq;
+#nullable disable
+
+using System.Xml.Linq;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Helpers/CSharpDefinitionFormatter.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;

src/MdDocs.ApiReference.Model/_Ids/ArrayTypeId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Ids/ByReferenceTypeId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Ids/EventId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Ids/FieldId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Ids/GenericTypeId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 

src/MdDocs.ApiReference.Model/_Ids/GenericTypeInstanceId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 using System.Collections.Generic;
 using System.Linq;
 

src/MdDocs.ApiReference.Model/_Ids/GenericTypeParameterId.cs

@@ -1,4 +1,6 @@
-using System;
+#nullable disable
+
+using System;
 
 namespace Grynwald.MdDocs.ApiReference.Model
 {

src/MdDocs.ApiReference.Model/_Ids/MemberId.cs

@@ -1,4 +1,6 @@
-using System.Collections.Generic;
+#nullable disable
+
+using System.Collections.Generic;
 using Grynwald.MdDocs.ApiReference.Model.XmlDocs;
 
 namespace Grynwald.MdDocs.ApiReference.Model