Thanks for your inquiry. I
have tested the scenario and have managed to reproduce the same issue at
my side. For the sake of correction, I have logged this problem in our
issue tracking system as WORDSNET-12579.
I have also tested this scenario using older version v15.1.0. The old version also throws the exception. However, the exception detail is different.
You will be notified via this forum thread once
this issue is resolved. We apologize for your inconvenience.