db_xml.py: put(): Indicate no parent_ids_loc using no_parent_ids_loc sentinel instead of None to support parent_ids_locs that are equal to None (e.g. if the parent node had an error). Always forward parent_ids_loc to children with fkeys to parent, even on error, because the parent table may not be required for the child tables to be valid, such as for taxonomic-data-only datasets that nevertheless have nodes for the non-taxonomic tables in their mappings.
db_xml.py: put(): Indicate no parent_ids_loc using no_parent_ids_loc sentinel instead of None to support parent_ids_locs that are equal to None (e.g. if the parent node had an error). Always forward parent_ids_loc to children with fkeys to parent, even on error, because the parent table may not be required for the child tables to be valid, such as for taxonomic-data-only datasets that nevertheless have nodes for the non-taxonomic tables in their mappings.