parentTermMap instead of reference

[ghsnd]

Issue type: :bug: Bug

Description

When using references in functions, a rml:parentTermap gets generated instead of a rml:reference.

Steps

Generate RML from test/condition-function-on-po/mapping.rml.ttl

The resulting RML looks like:

:om_007 rdf:type rr:ObjectMap ;
	rml:parentTermMap :ptm_000 .

:ptm_000 rml:reference "firstname" .

While it should look like:

:om_007 rdf:type rr:ObjectMap ;
	rml:reference "firstname" .

(This also makes test test/condition-function-on-po invalid)