Error: "Illegal property triple"

[TheRealMorgenfrue]

Describe the bug
When serializing FOAF, 23 triples (23 errors) failed to serialize with the error "Illegal property triple".

Happens both on main and #181.

To Reproduce
Steps to reproduce the behavior:

1. Load FOAF
2. Check Error Log in GUI or terminal

Expected behavior
No errors should be present.

Additional context
In most cases errors seem to be caused by reflexive owl:Ting, e.g.
Triple{ <http://www.w3.org/2002/07/owl#Thing> - <http://xmlns.com/foaf/0.1/phone> - <http://www.w3.org/2002/07/owl#Thing>