Fix hashtable initializer with no elements

If a hashtable expression does not contain elements it now generate
a `New` expression instead of a `ListInit` expression.

Author: SeeminglyScience

src/PSLambda/CompileVisitor.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
@@ -488,6 +488,14 @@ public object VisitForStatement(ForStatementAst forStatementAst)
 
         public object VisitHashtable(HashtableAst hashtableAst)
         {
+            if (hashtableAst.KeyValuePairs.Count == 0)
+            {
+                return New(
+                    ReflectionCache.Hashtable_Ctor,
+                    Constant(0),
+                    Property(null, ReflectionCache.StringComparer_CurrentCultureIgnoreCase));
+            }
+
             var elements = new ElementInit[hashtableAst.KeyValuePairs.Count];
             for (var i = 0; i < elements.Length; i++)
             {

test/MiscLanguageFeatures.Tests.ps1

@@ -6,6 +6,9 @@ Import-Module $manifestPath -Force
 Describe 'Misc Language Features' {
     It 'Hashtable expression' {
         $delegate = New-PSDelegate {
+    Context 'hashtable tests' {
+        It 'handles varied types of values' {
+            $delegate = New-PSDelegate {
             return @{
                 'string' = 'value'
                 string2 = 10
@@ -20,6 +23,11 @@ Describe 'Misc Language Features' {
         $hashtable['object'] | Should -BeOfType object
     }
 
+        It 'can initialize an empty hashtable' {
+            (New-PSDelegate { @{} }).Invoke().GetType() | Should -Be ([hashtable])
+        }
+    }
+
     Context 'array literal' {
         It 'int' {
             $result = (New-PSDelegate { 1, 2, 3 }).Invoke()