Attached is an OpenPGP certificate (dkg@aclu.org.key) which has three
User IDs, one of which is "dkg@aclu.org" but another has no e-mail
address at all (it's just "Daniel Kahn Gillmor").

From a new, empty user account, i did the following:

    gpg --batch --import < dkg@aclu.org.key

Then, in a new emacs window, in *scratch*, i ran the following:

    (require 'mml)
    (mml-secure-find-usable-keys (epg-make-context 'OpenPGP) "<dkg@aclu.org>" 'encrypt)

it crashes with the following backtrace:

Debugger entered--Lisp error: (wrong-type-argument char-or-string-p nil)
  mml-secure-check-user-id(#s(epg-key :owner-trust ultimate :sub-key-list (#s(epg-sub-key :validity ultimate :capability (sign certify) :secret-p nil :algorithm 1 :length 3072 :id "138F5AB68615C560" :creation-time (23350 . 32581) :expiration-time (24312 . 58949) :fingerprint "888E6BEAC41959269EAA177F138F5AB68615C560") #s(epg-sub-key :validity ultimate :capability (encrypt) :secret-p nil :algorithm 1 :length 3072 :id "9ED30DE244D1D77F" :creation-time (23350 . 32581) :expiration-time nil :fingerprint "9E2D1F76B4070A6BD4919CEA9ED30DE244D1D77F")) :user-id-list (#s(epg-user-id :validity ultimate :string "Daniel Kahn Gillmor" :signature-list nil) #s(epg-user-id :validity ultimate :string "dkgillmor@aclu.org" :signature-list nil) #s(epg-user-id :validity ultimate :string "dkg@aclu.org" :signature-list nil))) "<dkg@aclu.org>")
  mml-secure-find-usable-keys(#s(epg-context :protocol OpenPGP :program "/usr/bin/gpg2" :home-directory nil :armor nil :textmode nil :include-certs nil :cipher-algorithm nil :digest-algorithm nil :compress-algorithm nil :passphrase-callback (epg-passphrase-callback-function) :progress-callback nil :edit-callback nil :signers nil :sig-notations nil :process nil :output-file nil :result nil :operation nil :pinentry-mode nil :error-output "" :error-buffer nil) "<dkg@aclu.org>" encrypt)
  eval((mml-secure-find-usable-keys (epg-make-context 'OpenPGP) "<dkg@aclu.org>" 'encrypt) nil)


This appears to be because mml-secure-check-user-id chokes on the User
ID without any e-mail address.

The attached patch appears to fix the issue.  please include it in
emacs!

(i previously reported this to debian as https://bugs.debian.org/919642)

       --dkg



Configured using:
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ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
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Major mode: Lisp Interaction