plaza_preprocessing fails to handle plaza 538341606 with error: AttributeError: 'GeometryCollection' object has no attribute 'exterior'

[karme]

Hi,

I try to preprocess an extract of Hamburg. It fails with:

[INFO   ] - Processing plaza 5985547
[INFO   ] - Processing plaza 538341606
Traceback (most recent call last):
  File "/usr/local/bin/plaza_preprocessing", line 8, in <module>
    sys.exit(plaza_preprocessing())
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/__main__.py", line 22, in plaza_preprocessing
    preprocess_osm(source, destination, config)
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/__main__.py", line 31, in preprocess_osm
    processed_plazas = optimizer.preprocess_plazas(osm_holder, process_strategy, shortest_path_strategy, config)
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/optimizer/optimizer.py", line 20, in preprocess_plazas
    processed_plazas = plaza_processor.process_plazas()
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/optimizer/optimizer.py", line 45, in process_plazas
    processed_plaza = self._process_plaza(plaza)
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/optimizer/optimizer.py", line 73, in _process_plaza
    lookup_buffer_m=self.config['entry-point-lookup-buffer'])
  File "/usr/local/lib/python3.7/dist-packages/plaza_preprocessing/optimizer/optimizer.py", line 121, in _calc_entry_points
    plaza_outer_buffer = plaza_geometry.exterior.buffer(
AttributeError: 'GeometryCollection' object has no attribute 'exterior'
Command exited with non-zero status 1

The plaza in question looks harmless:
https://www.openstreetmap.org/way/538341606