Fix mypy errors

tomwhite · tomwhite · commit 68587f043aaf · 2024-04-30T16:34:20.000+01:00
diff --git a/flox/core.py b/flox/core.py
@@ -1754,6 +1754,7 @@ def cubed_groupby_agg(
 
     if method == "blockwise":
         assert by.ndim == 1
+        assert expected_groups is not None
 
         def _reduction_func(a, by, axis, start_group, num_groups):
             # adjust group labels to start from 0 for each chunk
