emacs-28 2963de6: * lisp/vc/vc-git.el (vc-git-mergebase): More meaningful error message.

[Juri Linkov]

branch: emacs-28
commit 2963de6540a1dc57399eaf530d8e12c794137a84
Author: Juri Linkov <juri@linkov.net>
Commit: Juri Linkov <juri@linkov.net>

    * lisp/vc/vc-git.el (vc-git-mergebase): More meaningful error message.
    
    Display a readable error message instead of signaling an error on nil value.
---
 lisp/vc/vc-git.el | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lisp/vc/vc-git.el b/lisp/vc/vc-git.el
index 3f89fad..2d35061 100644
--- a/lisp/vc/vc-git.el
+++ b/lisp/vc/vc-git.el
@@ -1256,7 +1256,10 @@ log entries."
 
 (defun vc-git-mergebase (rev1 &optional rev2)
   (unless rev2 (setq rev2 "HEAD"))
-  (string-trim-right (vc-git--run-command-string nil "merge-base" rev1 rev2)))
+  (let ((base (vc-git--run-command-string nil "merge-base" rev1 rev2)))
+    (if base
+        (string-trim-right base)
+      (error "No common ancestor for merge base"))))
 
 (defvar log-view-message-re)
 (defvar log-view-file-re)