HeaderMatchingFilter: Gracefully handle missing headers

[tohojo]

Notmuch can raise a NullPointerException when trying to read a non-existent header from a message. Gracefully handle this in the HeaderMatchingFilter by just aborting processing when encountering such an error.

[GuillaumeSeren]

Hello,
thank you for the patch.

This look like improvement to me but I would like this code to test covered,
do you mind adding a test for this ?

[tohojo]

Guillaume Seren ***@***.***> writes:

Hello, thank you for the patch. This look like improvement to me but I would like this code to test covered, do you mind adding a test for this ?

Sure, PTAL :)

[GuillaumeSeren]

Hey @tohojo ,
Thank you for the upgraded patch with the test support for this case.

It is LGTM 👍