comment-region fails if comment-padding is nil

[Jim Davidson]

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In GNU Emacs 21.1.1 (i386-msvc-nt4.0.1381)
 of 2001-10-22 on buffy
configured using `configure --with-msvc (12.00)'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: ENU
  locale-coding-system: iso-latin-1
  default-enable-multibyte-characters: nil

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

Set comment-padding to nil.

Do comment-region (e.g., in an elisp buffer).  This produces an error:

comment-region: Wrong type argument: arrayp, nil

The problem is an attempt to take a substring of nil.

nil is a valid value for comment-padding, according to the docstring
for the variable.  It worked in 20.7, but the comment code has been
rewritten since then.

Recent input:
C-a q u C-p c s A u C-k M-< C-n C-n C-n C-n C-n C-n 
C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-n C-y 
C-p C-p C-p C-p C-p C-p C-n C-n C-n C-n A s C-p C-p 
C-n C-n M-: ( s e t q SPC c o m m e n t - p a d d i 
n g SPC n i l ) <return> C-x 4 b . e m <tab> <return> 
C-p C-SPC C-p C-SPC C-n C-x ; M-x r e p o r t SPC e 
m <tab> <return>

Recent messages:
Saving file d:/News/.ggtesrc.eld...
Wrote d:/News/.ggtesrc.eld
Saving d:/News/.ggtesrc.eld...done
Killed group gnu.emacs.bug
Mark set
nil
Mark set [2 times]
Loading newcomment...done
comment-region: Wrong type argument: arrayp, nil
Loading emacsbug...done