Gen3 calib production for latiss fails due to empty SQL results due to missing entries in the `abstract_filter` table.  The query contains "... AND raw.abstract_filter = abstract_filter.name", which is always false when both sides are NULL.

The fast solution is to alter `obs_lsst`/filters.py to have abstract_filter="UNKNOWN" entries.  The correct solution probably is to force `obs_base` to require those entries when calling FilterDefinition.