Commands that treat empty lists as "all" should return no lists of a query that has zero results is passed

[cmungall]

In OAK, some commands will treat an empty list as "all"; e.g.

obi relationships

Shows all relationships in the ontology.

This behavior becomes confusing when the user passes a query via the OAK expression language and the query returns zero result. Currently no distinction is made between a zero-extent query result and zero terms passed by the user.

Zero-result queries should be treated differently from no input passed. The former should be treated as the true empty set.

Originally posted by @turbomam in #807 (comment)