[PATCH] Map missing content-type to "" instead of nil

[keithp at keithp.com]

From: Keith Packard <keithp at keithp.com>

When a message part has no content type, a 'nil' value results in many
failures when passed to functions like 'downcase'.  Instead of
crashing, map a nil value to the empty string, "", so that the show
operation doesn't crash.

Signed-off-by: Keith Packard <keithp at keithp.com>
---
 emacs/notmuch-show.el | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index e13ca3d7..7e3d0501 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -556,6 +556,10 @@ message at DEPTH in the current thread."
   "Alist from raw content ID to (MSG PART).")
 (make-variable-buffer-local 'notmuch-show--cids)
 
+(defun notmuch-show--plist-get(l m)
+  (let ((e (plist-get l m)))
+    (if e e "")))
+
 (defun notmuch-show--register-cids (msg part)
   "Register content-IDs in PART and all of PART's sub-parts."
   (let ((content-id (plist-get part :content-id)))
@@ -570,7 +574,7 @@ message at DEPTH in the current thread."
       (push (list content-id msg part) notmuch-show--cids)))
   ;; Recurse on sub-parts
   (let ((ctype (notmuch-split-content-type
-		(downcase (plist-get part :content-type)))))
+		(downcase (notmuch-show--plist-get part :content-type)))))
     (cond ((equal (first ctype) "multipart")
 	   (mapc (apply-partially #'notmuch-show--register-cids msg)
 		 (plist-get part :content)))
@@ -594,7 +598,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 	     ;; reference the same cid: part many times (hundreds!).
 	     (content (notmuch-get-bodypart-binary
 		       msg part notmuch-show-process-crypto 'cache))
-	     (content-type (plist-get part :content-type)))
+	     (content-type (notmuch-show--plist-get part :content-type)))
 	(list content content-type)))))
 
 (defun notmuch-show-setup-w3m ()
@@ -620,7 +624,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 ;; MIME part renderers
 
 (defun notmuch-show-multipart/*-to-list (part)
-  (mapcar (lambda (inner-part) (plist-get inner-part :content-type))
+  (mapcar (lambda (inner-part) (notmuch-show--plist-get inner-part :content-type))
 	  (plist-get part :content)))
 
 (defun notmuch-show-insert-part-multipart/alternative (msg part content-type nth depth button)
@@ -631,7 +635,7 @@ will return nil if the CID is unknown or cannot be retrieved."
     ;; but it's not clear that this is the wrong thing to do - which
     ;; should be chosen if there are more than one that match?
     (mapc (lambda (inner-part)
-	    (let* ((inner-type (plist-get inner-part :content-type))
+	    (let* ((inner-type (notmuch-show--plist-get inner-part :content-type))
 		  (hide (not (or notmuch-show-all-multipart/alternative-parts
 			   (string= chosen-type inner-type)))))
 	      (notmuch-show-insert-bodypart msg inner-part depth hide)))
@@ -948,7 +952,7 @@ will return nil if the CID is unknown or cannot be retrieved."
 
 (defun notmuch-show-mime-type (part)
   "Return the correct mime-type to use for PART."
-  (let ((content-type (downcase (plist-get part :content-type))))
+  (let ((content-type (downcase (notmuch-show--plist-get part :content-type))))
     (or (and (string= content-type "application/octet-stream")
 	     (notmuch-show-get-mime-type-of-application/octet-stream part))
 	(and (string= content-type "inline patch")
@@ -989,7 +993,7 @@ HIDE determines whether to show or hide the part and the button
 as follows: If HIDE is nil, show the part and the button. If HIDE
 is t, hide the part initially and show the button."
 
-  (let* ((content-type (downcase (plist-get part :content-type)))
+  (let* ((content-type (downcase (notmuch-show--plist-get part :content-type)))
 	 (mime-type (notmuch-show-mime-type part))
 	 (nth (plist-get part :id))
 	 (long (and (notmuch-match-content-type mime-type "text/*")
-- 
2.24.0.rc0