Fix issues with nullability and netstandard2.0

src/Spectre.Console.Cli/Internal/Binding/CommandValueResolver.cs

@@ -85,7 +85,7 @@ internal static class CommandValueResolver
                         }
 
                         // Assign the value to the parameter.
-                        binder.Bind(mapped.Parameter, resolver, converter.ConvertFromInvariantString(mapped.Value));
+                        binder.Bind(mapped.Parameter, resolver, converter.ConvertFromInvariantString(mapped.Value ?? string.Empty));
                     }
                 }
 
@@ -130,7 +130,13 @@ internal static class CommandValueResolver
             if (parameter.ParameterType.IsArray)
             {
                 // Return a converter for each array item (not the whole array)
-                return TypeDescriptor.GetConverter(parameter.ParameterType.GetElementType());
+                var elementType = parameter.ParameterType.GetElementType();
+                if (elementType == null)
+                {
+                    throw new InvalidOperationException("Could not get element type");
+                }
+
+                return TypeDescriptor.GetConverter(elementType);
             }
 
             if (parameter.IsFlagValue())

src/Spectre.Console.Cli/Internal/HelpWriter.cs

@@ -29,13 +29,13 @@ internal static class HelpWriter
 
     private sealed class HelpOption
     {
-        public string Short { get; }
+        public string? Short { get; }
-        public string Long { get; }
+        public string? Long { get; }
         public string? Value { get; }
         public bool? ValueIsOptional { get; }
         public string? Description { get; }
 
-        public HelpOption(string @short, string @long, string? @value, bool? valueIsOptional, string? description)
+        public HelpOption(string? @short, string? @long, string? @value, bool? valueIsOptional, string? description)
         {
             Short = @short;
             Long = @long;

src/Spectre.Console.Cli/Spectre.Console.Cli.csproj

@@ -17,7 +17,12 @@
     <InternalsVisibleTo Include="Spectre.Console.Cli.Tests" />
   </ItemGroup>
 
-  <ItemGroup>
+  <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <AnnotatedReferenceAssemblyVersion>3.0.0</AnnotatedReferenceAssemblyVersion>
+    <GenerateNullableAttributes>False</GenerateNullableAttributes>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160" PrivateAssets="all" />
     <PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[$(AnnotatedReferenceAssemblyVersion)]" />
     <PackageReference Include="Nullable" Version="1.3.1">
@@ -26,9 +31,4 @@
     </PackageReference>
   </ItemGroup>
 
-  <PropertyGroup>
-    <AnnotatedReferenceAssemblyVersion>3.0.0</AnnotatedReferenceAssemblyVersion>
-    <GenerateNullableAttributes>False</GenerateNullableAttributes>
-  </PropertyGroup>
-
 </Project>

src/Spectre.Console/Internal/TypeConverterHelper.cs

@@ -4,14 +4,20 @@ internal static class TypeConverterHelper
 {
     public static string ConvertToString<T>(T input)
     {
-        return GetTypeConverter<T>().ConvertToInvariantString(input);
+        var result = GetTypeConverter<T>().ConvertToInvariantString(input);
+        if (result == null)
+        {
+            throw new InvalidOperationException("Could not convert input to a string");
+        }
+
+        return result;
     }
 
-    public static bool TryConvertFromString<T>(string input, [MaybeNull] out T result)
+    public static bool TryConvertFromString<T>(string input, [MaybeNull] out T? result)
     {
         try
         {
-            result = (T)GetTypeConverter<T>().ConvertFromInvariantString(input);
+            result = (T?)GetTypeConverter<T>().ConvertFromInvariantString(input);
             return true;
         }
         catch
@@ -21,7 +27,7 @@ internal static class TypeConverterHelper
         }
     }
 
-    public static bool TryConvertFromStringWithCulture<T>(string input, CultureInfo? info, [MaybeNull] out T result)
+    public static bool TryConvertFromStringWithCulture<T>(string input, CultureInfo? info, [MaybeNull] out T? result)
     {
         try
         {
@@ -31,7 +37,7 @@ internal static class TypeConverterHelper
             }
             else
             {
-                result = (T)GetTypeConverter<T>().ConvertFromString(null!, info, input);
+                result = (T?)GetTypeConverter<T>().ConvertFromString(null!, info, input);
             }
 
             return true;

src/Spectre.Console/Spectre.Console.csproj

@@ -17,22 +17,25 @@
 
   <ItemGroup>
     <PackageReference Include="System.Memory" Version="4.5.5" />
+    <PackageReference Include="Wcwidth.Sources" Version="1.0.0">
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <PropertyGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
+    <AnnotatedReferenceAssemblyVersion>3.0.0</AnnotatedReferenceAssemblyVersion>
+    <GenerateNullableAttributes>False</GenerateNullableAttributes>
+  </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <PackageReference Include="TunnelVisionLabs.ReferenceAssemblyAnnotator" Version="1.0.0-alpha.160" PrivateAssets="all" />
     <PackageDownload Include="Microsoft.NETCore.App.Ref" Version="[$(AnnotatedReferenceAssemblyVersion)]" />
     <PackageReference Include="Nullable" Version="1.3.1">
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
-    <PackageReference Include="Wcwidth.Sources" Version="1.0.0">
-      <PrivateAssets>all</PrivateAssets>
-    </PackageReference>
   </ItemGroup>
 
-  <PropertyGroup>
-    <AnnotatedReferenceAssemblyVersion>3.0.0</AnnotatedReferenceAssemblyVersion>
-    <GenerateNullableAttributes>False</GenerateNullableAttributes>
-  </PropertyGroup>
-
   <PropertyGroup>
     <DefineConstants>$(DefineConstants)TRACE;WCWIDTH_VISIBILITY_INTERNAL</DefineConstants>
   </PropertyGroup>

src/Spectre.Console/Widgets/Figlet/FigletFontParser.cs

@@ -5,14 +5,20 @@ internal static class FigletFontParser
     public static FigletFont Parse(string source)
     {
         var lines = source.SplitLines();
-        var header = ParseHeader(lines.FirstOrDefault());
 
-        var characters = new List<FigletCharacter>();
+        var headerLine = lines.FirstOrDefault();
+        if (headerLine == null)
+        {
+            throw new InvalidOperationException("Could not read header line");
+        }
+
+        var header = ParseHeader(headerLine);
 
         var index = 32;
         var indexOverridden = false;
         var hasOverriddenIndex = false;
         var buffer = new List<string>();
+        var characters = new List<FigletCharacter>();
 
         foreach (var line in lines.Skip(header.CommentLines + 1))
         {

src/Spectre.Console/Widgets/Table/TableRowCollection.cs

@@ -107,8 +107,7 @@ public sealed class TableRowCollection : IReadOnlyList<TableRow>
                 throw new IndexOutOfRangeException("Table row index cannot exceed the number of rows in the table.");
             }
 
-            var tableRow = _list.ElementAtOrDefault(row);
+            var tableRow = _list.ElementAt(row);
-
             var currentRenderables = tableRow.ToList();
 
             if (column < 0)