Cannot convert null literal to non-nullable reference type.

Possible null reference argument for parameter 'key' in 'bool Dictionary<ClassDeclarationSyntax, SyntaxNode>.TryGetValue(ClassDeclarationSyntax key, out SyntaxNode value)'.

Cannot convert null literal to non-nullable reference type.

Possible null reference argument for parameter 'key' in 'bool Dictionary<ClassDeclarationSyntax, SyntaxNode>.TryGetValue(ClassDeclarationSyntax key, out SyntaxNode value)'.

Possible null reference argument for parameter 'document' in 'Task<ImmutableArray<Diagnostic>> FixAllContext.GetDocumentDiagnosticsAsync(Document document)'.

'DiagnosticAnalyzerExtensions.WithAnalyzers(Compilation, ImmutableArray<DiagnosticAnalyzer>, AnalyzerOptions?, CancellationToken)' is obsolete: 'Use WithAnalyzers overload without a cancellation token'

The type 'Microsoft.CodeAnalysis.CSharp.Syntax.MemberDeclarationSyntax?' cannot be used as type parameter 'TNode' in the generic type or method 'SyntaxFactory.List<TNode>(IEnumerable<TNode>)'. Nullability of type argument 'Microsoft.CodeAnalysis.CSharp.Syntax.MemberDeclarationSyntax?' doesn't match constraint type 'Microsoft.CodeAnalysis.SyntaxNode'.

Argument of type 'SyntaxList<MemberDeclarationSyntax?>' cannot be used for parameter 'members' of type 'SyntaxList<MemberDeclarationSyntax>' in 'ClassDeclarationSyntax ClassDeclarationSyntax.WithMembers(SyntaxList<MemberDeclarationSyntax> members)' due to differences in the nullability of reference types.

The type 'Microsoft.CodeAnalysis.CSharp.Syntax.MemberDeclarationSyntax?' cannot be used as type parameter 'TNode' in the generic type or method 'SyntaxFactory.List<TNode>(IEnumerable<TNode>)'. Nullability of type argument 'Microsoft.CodeAnalysis.CSharp.Syntax.MemberDeclarationSyntax?' doesn't match constraint type 'Microsoft.CodeAnalysis.SyntaxNode'.