TypeError when merging books 7.13

[James McIntosh]

After installing 7.13 on MacOS Sonoma 14.5, when trying to merge two books ("Merge into first selected book - delete others") I get the error "TypeError: cannot unpack non-iterable bool object".

Full details:

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

calibre 7.13 embedded-python: True
macOS-14.5-arm64-arm-64bit Darwin ('64bit', '')
('Darwin', '23.5.0', 'Darwin Kernel Version 23.5.0: Wed May 1 20:14:38 PDT 2024; root:xnu-10063.121.3~5/RELEASE_ARM64_T6020')
Python 3.11.5
OSX: ('14.5', ('', '', ''), 'arm64')
Interface language: None
EXE path: /Applications/calibre.app/Contents/MacOS/calibre
Successfully initialized third party plugins: Amazon.com Multiple Countries (1, 0, 0) && Barnes & Noble (1, 5, 5) && BookFusion Plugin (0, 8, 1) && FictionDB (1, 4, 2) && Find Duplicates (1, 10, 9) && Goodreads (1, 8, 2) && Kindle hi-res covers (0, 5, 1) && Quality Check (1, 13, 11)
Traceback (most recent call last):
  File "calibre/gui2/actions/edit_metadata.py", line 644, in merge_books
TypeError: cannot unpack non-iterable bool object