Fix demands undo bug

api/s9_demands.py

@@ -44,8 +44,8 @@ def set_demand_cache(name: str, cs: ChangeSet) -> BatchSqlChangeSet:
     _undo_sql = f"delete from demands where junction = {f_junction};"
     for r in old['demands']:
         demand = float(r['demand'])
-        pattern = str(r['pattern'])
-        category = str(r['category'])
+        pattern = str(r['pattern']) if 'pattern' in r and r['pattern'] != None else None
+        category = str(r['category']) if 'category' in r and r['category'] != None else None
         f_demand = demand
         f_pattern = f"'{pattern}'" if pattern != None else 'null'
         f_category = f"'{category}'" if category != None else 'null'