Fix obvious schema issue

src/calng/stacking_utils.py

@@ -8,6 +8,7 @@ from karabo.bound import (
     TABLE_ELEMENT,
     Hash,
     Schema,
+    State,
 )
 import numpy as np
 
@@ -87,7 +88,7 @@ class StackingFriend:
     @staticmethod
     def add_schema(self, schema):
         (
-            TABLE_ELEMENT(expected)
+            TABLE_ELEMENT(schema)
             .key("merge")
             .displayedName("Array stacking")
             .allowedStates(State.PASSIVE)