Bug: Code Generation RDF4 with a Preserve option

[charbull]

Describe the bug Some classes are not being generated with RDF4J with the preserve namespace option code generation.

To Reproduce

1. use the digital buildings ontology: https://github.com/google/digitalbuildings/blob/master/ontology/rdf/digital_buildings.rdf
2. generate OLGA in Java with -preserve --code java --library rdf4j --name DigitalBuildings --path PATH_TO_ONTOLOGY
3. See error

Expected behavior Some Classes are not being generated,

Desktop (please complete the following information):

• OS: MacOS or Ubuntu