(risky-local-variable-p): VAL=nil has special meaning.

1 files changed, 4 insertions, 2 deletions

diff --git a/lisp/files.el b/lisp/files.el
index be6cdfeb9b7..f050713e135 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2061,7 +2061,8 @@ is specified, returning t if it is specified."
 (put 'compile-command 'safe-local-variable 'stringp)
 
 (defun risky-local-variable-p (sym val)
-  "Non-nil if SYM could be dangerous as a file-local variable with value VAL."
+  "Non-nil if SYM could be dangerous as a file-local variable with value VAL.
+If VAL is nil, the question is whether any value might be dangerous."
   (let ((safep (get sym 'safe-local-variable)))
     (or (memq sym ignored-local-variables)
         (get sym 'risky-local-variable)
@@ -2071,7 +2072,8 @@ is specified, returning t if it is specified."
         ;; If the safe-local-variable property isn't t or nil,
         ;; then it must return non-nil on the proposed value to be safe.
         (and (not (memq safep '(t nil)))
-             (not (funcall safep val))))))
+             (or (null val)
+                 (not (funcall safep val)))))))
 
 (defcustom safe-local-eval-forms nil
   "*Expressions that are considered \"safe\" in an `eval:' local variable.