master 95f7a28: Fix Elisp's elisp--documentation-one-liner (bug#43609)

[João Távora]

branch: master
commit 95f7a2835a79c1f12b5dc86230405e8040910c72
Author: João Távora <joaotavora@gmail.com>
Commit: João Távora <joaotavora@gmail.com>

    Fix Elisp's elisp--documentation-one-liner (bug#43609)
    
    To be backward compatible, this function must return nil when there is
    a symbol at point but no documentation for it.  Before this fixed it
    returned the string "<symbol-name>: nil".
    
    * lisp/progmodes/elisp-mode.el (elisp--documentation-one-liner):
    Check callback actually produced non-nil doc.
---
 lisp/progmodes/elisp-mode.el | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index ce2b924..12788ea 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -1416,12 +1416,13 @@ which see."
 (defun elisp--documentation-one-liner ()
   (let* (str
          (callback (lambda (doc &rest plist)
-                     (setq str
-                           (format "%s: %s"
-                                   (propertize (prin1-to-string
-                                                (plist-get plist :thing))
-                                               'face (plist-get plist :face))
-                                   doc)))))
+                     (when doc
+                       (setq str
+                             (format "%s: %s"
+                                     (propertize (prin1-to-string
+                                                  (plist-get plist :thing))
+                                                 'face (plist-get plist :face))
+                                     doc))))))
     (or (progn (elisp-eldoc-var-docstring callback) str)
         (progn (elisp-eldoc-funcall callback) str))))