diff --git a/src/Elmah.MongoDB/NameValueCollectionSerializer.cs b/src/Elmah.MongoDB/NameValueCollectionSerializer.cs
index b19b31b..1056295 100644
--- a/src/Elmah.MongoDB/NameValueCollectionSerializer.cs
+++ b/src/Elmah.MongoDB/NameValueCollectionSerializer.cs
@@ -57,18 +57,17 @@ public override void Serialize(
 			IBsonSerializationOptions options
 			)
 		{
-			if (value == null)
+            var nvc = value as NameValueCollection;
+            if (nvc == null)
 			{
 				bsonWriter.WriteNull();
 				return;
 			}
 
-			var nvc = (NameValueCollection)value;
-
 			bsonWriter.WriteStartArray();
 			foreach (var key in nvc.AllKeys)
 			{
-				foreach (var val in nvc.GetValues(key))
+                foreach (var val in nvc.GetValues(key) ?? new string[0])
 				{
 					bsonWriter.WriteStartArray();
 					StringSerializer.Instance.Serialize(bsonWriter, typeof(string), key, options);