Comment 1 for bug 2071520

Same Issue. Started after a recent update.

Seecting two books and pressing M to merge.

calibre, version 7.13.0
ERROR: Unhandled exception: <b>TypeError</b>:cannot unpack non-iterable bool object

calibre 7.13 embedded-python: True
Windows-10-10.0.19045-SP0 Windows ('64bit', 'WindowsPE')
('Windows', '10', '10.0.19045')
Python 3.11.5
Windows: ('10', '10.0.19045', 'SP0', 'Multiprocessor Free')
Interface language: None
EXE path: C:\Program Files\Calibre2\calibre.exe
Successfully initialized third party plugins: Find Duplicates (1, 10, 9)
Traceback (most recent call last):
  File "calibre\gui2\actions\edit_metadata.py", line 644, in merge_books
TypeError: cannot unpack non-iterable bool object