System.Collections.Immutable.ImmutableDictionary<TKey, TValue>

public sealed class ImmutableDictionary<TKey, TValue> : IImmutableDictionary<TKey, TValue>, IReadOnlyDictionary<TKey, TValue>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, IEnumerable, IImmutableDictionaryInternal<TKey, TValue>, IHashKeyCollection<TKey>, IDictionary<TKey, TValue>, ICollection<KeyValuePair<TKey, TValue>>, IDictionary, ICollection

/* Error decompiling System.Collections.Generic.IEnumerable`1 System.Collections.Immutable.ImmutableDictionary`2/Builder::get_Keys() ---> System.InvalidOperationException: Cannot mutate frozen NullBlockStatement at ICSharpCode.Decompiler.CSharp.Syntax.AstNode.AddChild[T](T child, Role`1 role) in offset 36 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileBody(MethodDefinition methodDefinition, IMethod method, EntityDeclaration entityDecl, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in offset 637 -- continuing with outer exception (ICSharpCode.Decompiler.DecompilerException) -- at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileBody(MethodDefinition methodDefinition, IMethod method, EntityDeclaration entityDecl, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in offset 835 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(PropertyDefinition propertyDefinition, IProperty property, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in offset 0 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in offset 327 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompile(ITypeDefinition typeDef, DecompileRun decompileRun, ITypeResolveContext decompilationContext) in offset 84 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DoDecompileTypes(IEnumerable`1 types, DecompileRun decompileRun, ITypeResolveContext decompilationContext, SyntaxTree syntaxTree) in offset 173 at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileType(FullTypeName fullTypeName) in offset 141 at Relativity.APIReference.TypeDocumentation.b__30_0() in TypeDocumentation.cs:line 270 */