Added guards to ICollection.CopyTo implementations to avoid allocating the indices array for SetValue when the collection being copied from is empty

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary`2+Builder.cs

@@ -345,6 +345,11 @@ namespace System.Collections.Immutable
                 Requires.Range(arrayIndex >= 0, "arrayIndex");
                 Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+                if (count == 0) 
+                {
+                    return;
+                }
+
                 int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
                 foreach (var item in this)
                 {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableDictionary`2.cs

@@ -780,6 +780,11 @@ namespace System.Collections.Immutable
             Requires.Range(arrayIndex >= 0, "arrayIndex");
             Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+            if (count == 0) 
+            {
+                return;
+            }
+
             int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
             foreach (var item in this)
             {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableHashSet`1.cs

@@ -562,6 +562,11 @@ namespace System.Collections.Immutable
             Requires.Range(arrayIndex >= 0, "arrayIndex");
             Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+            if (count == 0)
+            {
+                return;
+            }
+
             int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
             foreach (T item in this)
             {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableList`1.cs

@@ -2590,6 +2590,11 @@ namespace System.Collections.Immutable
                 Requires.Range(arrayIndex >= 0, "arrayIndex");
                 Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+                if (count == 0)
+                {
+                    return;
+                }
+
                 int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
                 foreach (var element in this)
                 {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedDictionary`2.cs

@@ -1381,6 +1381,11 @@ namespace System.Collections.Immutable
                 Requires.Range(arrayIndex >= 0, "arrayIndex");
                 Requires.Range(array.Length >= arrayIndex + dictionarySize, "arrayIndex");
 
+                if (IsEmpty)
+                {
+                    return;
+                }
+
                 int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
                 foreach (var item in this)
                 {

src/System.Collections.Immutable/src/System/Collections/Immutable/ImmutableSortedSet`1.cs

@@ -1689,6 +1689,11 @@ namespace System.Collections.Immutable
                 Requires.Range(arrayIndex >= 0, "arrayIndex");
                 Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+                if (IsEmpty)
+                {
+                    return;
+                }
+
                 int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
                 foreach (var item in this)
                 {

src/System.Collections.Immutable/src/System/Collections/Immutable/KeysOrValuesCollectionAccessor.cs

@@ -139,6 +139,11 @@ namespace System.Collections.Immutable
             Requires.Range(arrayIndex >= 0, "arrayIndex");
             Requires.Range(array.Length >= arrayIndex + this.Count, "arrayIndex");
 
+            if (Count == 0)
+            {
+                return;
+            }
+
             int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
             foreach (T item in this)
             {

src/System.Xml.XmlDocument/src/System/Xml/Dom/XmlAttributeCollection.cs

@@ -246,6 +246,11 @@ namespace System.Xml
 
         void ICollection.CopyTo(Array array, int index)
         {
+            if (Count == 0)
+            {
+                return;
+            }
+
             int[] indices = new int[1]; // SetValue takes a params array; lifting out the implicit allocation from the loop
             for (int i = 0, max = Count; i < max; i++, index++)
             {