Update after review (#1178)

* Updates after review

* Remove EmptyArray

Author: slozier

Src/IronPython/Compiler/Ast/CallExpression.cs

@@ -176,7 +176,7 @@ static MSAst.Expression UnpackDictHelper(MSAst.Expression context, ReadOnlySpan<
                 expressions.Add(Expression.Assign(varExpr, Expression.Call(AstMethods.MakeEmptyDict)));
                 foreach (var arg in kwargs) {
                     if (arg.Name is null) {
-                        expressions.Add(Expression.Call(AstMethods.DictMerge, context, varExpr, arg.Expression));
+                        expressions.Add(Expression.Call(AstMethods.DictMerge, context, varExpr, AstUtils.Convert(arg.Expression, typeof(object))));
                     }
                 }
                 expressions.Add(varExpr);

Src/IronPython/Compiler/Ast/ClassDefinition.cs

@@ -222,12 +222,12 @@ static MSAst.Expression UnpackBasesHelper(ReadOnlySpan<Expression> bases) {
             }
 
             // Compare to: CallExpression.Reduce.__UnpackDictHelper
-            static MSAst.Expression UnpackKeywordsHelper(MSAst.Expression context, IReadOnlyList<Keyword> kwargs) {
-                if (kwargs.Count == 0) {
+            static MSAst.Expression UnpackKeywordsHelper(MSAst.Expression context, ReadOnlySpan<Keyword> kwargs) {
+                if (kwargs.Length == 0) {
                     return AstUtils.Constant(null, typeof(PythonDictionary));
                 }
 
-                var expressions = new ReadOnlyCollectionBuilder<MSAst.Expression>(kwargs.Count + 2);
+                var expressions = new ReadOnlyCollectionBuilder<MSAst.Expression>(kwargs.Length + 2);
                 var varExpr = Expression.Variable(typeof(PythonDictionary), "$dict");
                 expressions.Add(Expression.Assign(varExpr, Expression.Call(AstMethods.MakeEmptyDict)));
                 foreach (var arg in kwargs) {

Src/IronPython/Compiler/Ast/Expression.cs

@@ -19,8 +19,6 @@
 
 namespace IronPython.Compiler.Ast {
     public abstract class Expression : Node {
-        internal static readonly Expression[] EmptyArray = Array.Empty<Expression>();
-
         protected internal static MSAst.BlockExpression UnpackSequenceHelper<T>(ReadOnlySpan<Expression> items, MethodInfo makeEmpty, MethodInfo append, MethodInfo extend) {
             var expressions = new ReadOnlyCollectionBuilder<MSAst.Expression>(items.Length + 2);
             var varExpr = Expression.Variable(typeof(T), "$coll");

Src/IronPython/Compiler/Ast/Keyword.cs

@@ -4,26 +4,26 @@
 
 #nullable enable
 
-using Microsoft.Scripting.Actions;
+using System;
 
 namespace IronPython.Compiler.Ast {
     public class Keyword : Node {
         public Keyword(string? name, Expression expression) {
             Name = name;
-            Expression = expression;
+            Expression = expression ?? throw new ArgumentNullException(nameof(expression));
         }
 
         public string? Name { get; }
 
         public Expression Expression { get; }
 
         public override string ToString() {
-            return base.ToString() + ":" + Name;
+            return base.ToString() + ":" + (Name ?? "**{...}");
         }
 
         public override void Walk(PythonWalker walker) {
             if (walker.Walk(this)) {
-                Expression?.Walk(walker);
+                Expression.Walk(walker);
             }
             walker.PostWalk(this);
         }