master 1e3a7bf69d 1/2: avoid error when message-fetch-field returns nil

[Sam Steingold]

branch: master
commit 1e3a7bf69d05dbbe5c853780f18caf81f1e22d32
Author: Sam Steingold <sds@gnu.org>
Commit: Sam Steingold <sds@gnu.org>

    avoid error when message-fetch-field returns nil
    
    * gnus-art.el (article-hide-boring-headers): Use "" when
      `message-fetch-field' returns `nil'
---
 lisp/gnus/gnus-art.el | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lisp/gnus/gnus-art.el b/lisp/gnus/gnus-art.el
index e28d84e06f..18baf982b2 100644
--- a/lisp/gnus/gnus-art.el
+++ b/lisp/gnus/gnus-art.el
@@ -1987,8 +1987,8 @@ always hide."
                  (gnus-article-hide-header "cc"))))
             ((eq elem 'followup-to)
              (when (string-equal-ignore-case
-                    (message-fetch-field "followup-to")
-                    (message-fetch-field "newsgroups"))
+                    (or (message-fetch-field "followup-to") "")
+                    (or (message-fetch-field "newsgroups") ""))
                (gnus-article-hide-header "followup-to")))
             ((eq elem 'reply-to)
              (if (gnus-group-find-parameter