Why does “No Star” cause an error when saving hotel details?

[bluemoon288]

In QloApps 1.7 the hotel star selection includes “No Star” alongside 1–5 stars.
When I select “No Star” and try to save, I get an error saying the field is required.
Many hotels are not officially classified, so selecting “No Star” should be possible.
Is this a bug, or is there another way to save a hotel without a star rating?
Thanks for your help!