bug#26298: 26.0.50; Gnus fails to sign mail with PGP

[Toon Claes]

Torsten Bronger <bronger@physik.rwth-aachen.de> writes:

> If I sign an email with C-c RET s o and try to send it, Emacs aborts
> with the following backtrace:
>
> Debugger entered--Lisp error: (wrong-type-argument char-or-string-p
> nil)

I am getting the same error. 

I am using the following line to trigger my mails being signed:

<#secure method=pgpmime mode=sign>

Another thing I've noticed. When I manually sign a file with
epa-sign-file, it asks my passphrase and signs the file correctly.
When I afterwards try to send a signed mail, it is also signed
correctly. So it seems pinentry is failing, not the signing itself.

I'm having this problem for quite some time, and I am frequently
building a new emacs from master.

My current version:

GNU Emacs 26.0.50 (build 2, x86_64-apple-darwin16.6.0, NS appkit-1504.83
Version 10.12.5 (Build 16F73)) of 2017-06-26 

-- Toon