diff --git a/src/runtime/assemblymanager.cs b/src/runtime/assemblymanager.cs
index a217e84e2..e528ca118 100644
--- a/src/runtime/assemblymanager.cs
+++ b/src/runtime/assemblymanager.cs
@@ -357,7 +357,7 @@ public static AssemblyName[] ListAssemblies()
         //===================================================================
 
         public static bool IsValidNamespace(string name) {
-            return namespaces.ContainsKey(name);
+            return !String.IsNullOrEmpty(name) && namespaces.ContainsKey(name);
         }
 
         //===================================================================