convert enumerate/generator into list before checking it't not empty (#32259)

wcs_olap/feeder.py

@@ -402,8 +402,11 @@ CREATE TABLE public.dates AS (SELECT
                 ids = range(next_id, next_id + len(to_insert))
                 labels = zip(ids, to_insert)
 
-        if labels:
+        if labels is not None:
+            # turn enumerate generator object into a proper list
             labels = list(labels)
+
+        if labels:
             tmpl = ', '.join(['(%s, %s)'] * len(labels))
             query_str = 'INSERT INTO {name} (id, label) VALUES %s' % tmpl
             self.ex(query_str, ctx={'name': name}, vars=list(itertools.chain(*labels)))