Jura Z7 "Fill beans" is not displayed

Hello everyone, maybe you can help me. I own a Jura Z7. For some time now, the message Fill beans no longer appears. When the container is empty I always hear it at the grinder that there is nothing left inside. I also know it's not good for the grinder. Is it possible that a sensor is contaminated somewhere? If so, where can I find this one? Is it an expensive problem? I thank you in advance and look forward to your help. Best
regards Astrid

The active bean monitoring system may be contaminated by coffee oil.
Wipe the sensor with a cotton cloth or
ask
the service hotline for an authorized workshop near you
.

Thank you very much for the answer.
Where do I find the sensor?

In bean containers.