diff --git a/lib/config/configitem.cpp b/lib/config/configitem.cpp
index a6c959e58..8a14de5aa 100644
--- a/lib/config/configitem.cpp
+++ b/lib/config/configitem.cpp
@@ -521,8 +521,6 @@ bool ConfigItem::CommitItems(const ActivationContext::Ptr& context, WorkQueue& u
 		return false;
 	}
 
-	ASSERT(newItems.size() > 0);
-
 	ApplyRule::CheckMatches();
 
 	/* log stats for external parsers */
@@ -593,6 +591,9 @@ bool ConfigItem::RunWithActivationContext(const Function::Ptr& function)
 {
 	ActivationScope scope;
 
+	if (!function)
+		BOOST_THROW_EXCEPTION(ScriptError("'function' argument must not be null."));
+
 	{
 		ScriptFrame frame;
 		function->Invoke();