1 files changed, 33 insertions, 5 deletions
diff --git a/src/ProtocolBuffers/Collections/PopsicleList.cs b/src/ProtocolBuffers/Collections/PopsicleList.cs
index dc5c5836..3de97f89 100644
--- a/src/ProtocolBuffers/Collections/PopsicleList.cs
+++ b/src/ProtocolBuffers/Collections/PopsicleList.cs
@@ -42,6 +42,7 @@ namespace Google.ProtocolBuffers.Collections
     /// </summary>
     public sealed class PopsicleList<T> : IPopsicleList<T>, ICastArray
     {
+        private static readonly bool CheckForNull = default(T) == null;
         private static readonly T[] EmptySet = new T[0];
 
         private List<T> items;
@@ -65,6 +66,10 @@ namespace Google.ProtocolBuffers.Collections
         public void Insert(int index, T item)
         {
             ValidateModification();
+            if (CheckForNull)
+            {
+                ThrowHelper.ThrowIfNull(item);
+            }
             items.Insert(index, item);
         }
 
@@ -87,6 +92,10 @@ namespace Google.ProtocolBuffers.Collections
             set
             {
                 ValidateModification();
+                if (CheckForNull)
+                {
+                    ThrowHelper.ThrowIfNull(value);
+                }
                 items[index] = value;
             }
         }
@@ -94,6 +103,10 @@ namespace Google.ProtocolBuffers.Collections
         public void Add(T item)
         {
             ValidateModification();
+            if (CheckForNull)
+            {
+                ThrowHelper.ThrowIfNull(item);
+            }
             items.Add(item);
         }
 
@@ -145,15 +158,30 @@ namespace Google.ProtocolBuffers.Collections
 
         public void Add(IEnumerable<T> collection)
         {
-            if (readOnly)
+            ValidateModification();
+            ThrowHelper.ThrowIfNull(collection);
+
+            if (!CheckForNull || collection is PopsicleList<T>)
             {
-                throw new NotSupportedException("List is read-only");
+                items.AddRange(collection);
             }
-            if (items == null)
+            else
             {
-                items = new List<T>();
+                // Assumption, it's ok to enumerate collections more than once.
+                if (collection is ICollection<T>)
+                {
+                    ThrowHelper.ThrowIfAnyNull(collection);
+                    items.AddRange(collection);
+                }
+                else
+                {
+                    foreach (T item in collection)
+                    {
+                        ThrowHelper.ThrowIfNull(item);
+                        items.Add(item);
+                    }
+                }
             }
-            items.AddRange(collection);
         }
 
         private void ValidateModification()