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validate slicelike return hint

Co-authored-by: Jacob Wilkins <[email protected]>

janus_core/helpers/utils.py

@@ -416,7 +416,7 @@ def track_progress(sequence: Sequence | Iterable, description: str) -> Iterable:
         yield from progress.track(sequence, description=description)
 
 
-def validate_slicelike(maybe_slicelike: SliceLike):
+def validate_slicelike(maybe_slicelike: SliceLike) -> None:
     """
     Raise an exception if slc is not a valid SliceLike.