bug#54443: 29.0.50; decipher.el: (wrong-type-argument bufferp nil) when calling decipher-digram-list (and others)

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 18 Mar 2022 07:37:44 +0000
> From: Simon Pugnet <simon@polaris64.net>
> 
> I recently found out about the decipher package, but when trying it I
> get the following error: -
> 
> Debugger entered--Lisp error: (wrong-type-argument bufferp nil)
>   decipher-stats-buffer(t)
>   decipher-analyze-buffer()
>   decipher-analyze()
>   decipher-digram-list()
>   funcall-interactively(decipher-digram-list)
>   command-execute(decipher-digram-list)
> 
> To reproduce: -
> 
> 1. emacs -Q
> 2. M-x decipher
> 3. Press D to call decipher-digram-list

Thanks.  Does the patch below give good results?

diff --git a/lisp/play/decipher.el b/lisp/play/decipher.el
index ae44ecd..aeb4726 100644
--- a/lisp/play/decipher.el
+++ b/lisp/play/decipher.el
@@ -983,13 +983,14 @@ decipher-stats-buffer
     decipher-stats-buffer)
    ;; Create a new buffer if requested:
    (create
-    (let ((stats-name (concat "*" (buffer-name) "*")))
+    (let* ((stats-name (concat "*" (buffer-name) "*"))
+           (buf (get-buffer stats-name)))
       (setq decipher-stats-buffer
-            (if (eq 'decipher-stats-mode
-                    (buffer-local-value 'major-mode
-                                        (get-buffer stats-name)))
-                ;; We just lost track of the statistics buffer:
-                (get-buffer stats-name)
+            (if (and (bufferp buf)
+                     (eq 'decipher-stats-mode
+                         (buffer-local-value 'major-mode buf)))
+                buf
+              ;; We just lost track of the statistics buffer:
               (generate-new-buffer stats-name))))
     (with-current-buffer decipher-stats-buffer
       (decipher-stats-mode))