Running a chain (by accident, admittedly) with "Open with: Book format" (default application) errors if the book doesn't have the specified format.
Code:
Traceback (most recent call last):
File "calibre_plugins.action_chains.action", line 237, in run_chain
File "calibre_plugins.action_chains.chain_tools", line 120, in run_loop
File "calibre_plugins.action_chains.chain_tools", line 100, in run_loop
File "calibre_plugins.action_chains.actions.open_with", line 309, in run
File "calibre\gui2\__init__.py", line 1297, in open_local_file
File "ntpath.py", line 452, in normpath
TypeError: expected str, bytes or os.PathLike object, not NoneType