deal with model_info is none (#253)

* make sure the model_info_dict defaults to an empty dict

* Update rosys/vision/detector_hardware.py

Co-authored-by: Falko Schindler <falko@zauberzeug.com>

---------

Co-authored-by: Niklas Neugebauer <68709968+NiklasNeugebauer@users.noreply.github.com>
Co-authored-by: Falko Schindler <falko@zauberzeug.com>

rosys/vision/detector_hardware.py

@@ -198,7 +198,7 @@ async def fetch_detector_info(self) -> DetectorInfo:
             raise DetectorException('Invalid response from detector')
 
         try:
-            model_info_dict = response.get('model_info', {})
+            model_info_dict = response.get('model_info') or {}
             return DetectorInfo(
                 operation_mode=response['operation_mode'],
                 state=response.get('state'),