null returndoctype fails to return all documents
When the pathquery "returndoctype" filed is omitted, metacat is supposed to
return all matching documents. In fact, no documents are returned under version
1.3.1, because it filters out all documents in the returndoctype listt is empty
or null. Fixing this will require chaning the logic in the DBQuery module to
include results even when the returndoctype field is not present.