Apply downloaded metadata crashes after review

[Florian Sieghart]

OS: Windows 7 Ultimate 64bit
calibre, version 0.9.29 Windows 64bit

Selected 6-7 books, select "download metadata", "metadata only", "review metadata", "...next" until last book, then metadata routine crashes with following error message and the metadata is not applied:

ERROR: Unhandled exception: <b>TypeError</b>:coercing to Unicode: need string or buffer, NoneType found

Traceback (most recent call last):
  File "site-packages\calibre\gui2\proceed.py", line 118, in do_ask_question
  File "site-packages\calibre\gui2\actions\edit_metadata.py", line 246, in apply_downloaded_metadata
  File "shutil.py", line 73, in copyfile
TypeError: coercing to Unicode: need string or buffer, NoneType found

Happened several times now (not sure if exactly same error message). Inbetween it works fine.

[Florian Sieghart (florian-sieghart)]

Additional information: it only happens - but then always - if in the review window the existing cover is selected and copied to the left side, i.e. the downloaded metadata.

Doing this is not necessary, since the left cover field is empty ("metadata only") and for empty values, the original value is taken automatically, but this seems to be the culprit.