When model_name, bucketfs_conn, or sub_dir are NULL the function extract_unique_model_dataframes_from_batch returns an empty dataframe which will lead to the following error message RuntimeError: E-UDF-CL-SL-PYTHON-1087: emit DataFrame is empty
model_name, bucketfs_conn, or sub_dir can't be really empty, for that reason failing is actually correct, but we should give a better error message what is wrong
Background
RuntimeError: E-UDF-CL-SL-PYTHON-1087: emit DataFrame is empty