A sort spec (FieldKey-asc / FieldKey-desc): not blank. A blank one would go
out as sort= (the same as no sort) or sort=%20%20, and an explicitly blank
sort is a mistake rather than a request for the default order. The shape itself is
left to the register: it refused an unknown sort key with {"Error":true} (live
2026-10-09; it used to answer 0 rows), which the client turns into a MastrApiError.
A
sortspec (FieldKey-asc/FieldKey-desc): not blank. A blank one would go out assort=(the same as no sort) orsort=%20%20, and an explicitly blank sort is a mistake rather than a request for the default order. The shape itself is left to the register: it refused an unknown sort key with{"Error":true}(live 2026-10-09; it used to answer 0 rows), which the client turns into a MastrApiError.