More informative error when subsetting results in no observations retained in Visium HD

[matt-sd-watson]

When filtering bin spots in Visium HD, when using a sufficiently large expression filter:

mask = (sdata.tables[table].X > 0).sum(axis=1).A1 >= 500

The resulting table, if filtered using the mask, would contain no observations.

However, the error provided does not indicate this, and instead suggests a different type of data mismatch:

schema = get_model(value)
  File "/home/admin/.local/lib/python3.10/site-packages/spatialdata/models/models.py", line 1195, in get_model
    return _validate_and_return(TableModel, e)
  File "/home/admin/.local/lib/python3.10/site-packages/spatialdata/models/models.py", line 1178, in _validate_and_return
    schema().validate(e)
  File "/home/admin/.local/lib/python3.10/site-packages/spatialdata/models/models.py", line 1056, in validate
    self._validate_table_annotation_metadata(data)
  File "/home/admin/.local/lib/python3.10/site-packages/spatialdata/models/models.py", line 1034, in _validate_table_annotation_metadata
    raise ValueError(f"Regions in the AnnData object and `{attr[self.REGION_KEY_KEY]}` do not match.")
ValueError: Regions in the AnnData object and `region` do not match.

It may be useful to first have a check that the relevant table is non-empty before throwing this ValueError, as it suggested to be that a metadata column was corrupted or removed during processing.