FIX: keyError when only one record has datatype, unit or value

src/caosdb/apiutils.py

@@ -338,7 +338,10 @@ def merge_entities(entity_a: Entity, entity_b: Entity):
                 raise NotImplementedError()
 
             for attribute in ("datatype", "unit", "value"):
-                if diff_r1["properties"][key][attribute] is None:
+                if (attribute in diff_r2["properties"][key] and
+                        diff_r2["properties"][key][attribute] is not None):
+                    print(diff_r2["properties"][key][attribute])
+                    if (diff_r1["properties"][key][attribute] is None):
                         setattr(entity_a.get_property(key), attribute,
                                 diff_r2["properties"][key][attribute])
                     else: