bug#25194: 25.1; Python debugger breakpoint error

[Live System User <nyc4bos@aol.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Live System User <nyc4bos@aol.com>
>> Date: Tue, 13 Dec 2016 05:10:03 -0500
>> 
>> 4. Cick on "Set Breakpoint"
>> 
>>    I now get the error:
>>    
>>       Wrong type argument: stringp, nil
>> 
>>    Turning on `debug-on-error' yields the same results.
>>    However, on the *Messages* buffer there is a little more
>>    information about the error:
>> 
>>        gud-format-command: Wrong type argument: stringp, nil
>> 
>>    How does one debug this problem further?
>
> Did you try debug-on-entry?

  Thanks!

  I never used this command before -- so I tried it:

     M-x debug-on-entry RET gud-break

     When trying to set a breakpoint, I got a *Backtrace*:

Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  file-name-directory(nil)
  gud-format-command("break %d%f:%l" 4)
  gud-call("break %d%f:%l" 4)
  #[257 "\b?\205	\301\302\"\207" [gud-running gud-call "break %d%f:%l"] 4 "Set breakpoint at current line.\n\n(fn ARG)" "p"](4)
  apply(#[257 "\b?\205	\301\302\"\207" [gud-running gud-call "break %d%f:%l"] 4 "Set breakpoint at current line.\n\n(fn ARG)" "p"] 4)
  gud-break(4)
  eval((gud-break 4) nil)
  eval-expression((gud-break 4) nil)
  funcall-interactively(eval-expression (gud-break 4) nil)
  call-interactively(eval-expression nil nil)
  command-execute(eval-expression)
  recursive-edit()
  debug(debug)
  debug--implement-debug-on-entry(1)
  apply(debug--implement-debug-on-entry 1)
* gud-break(1)
  funcall-interactively(gud-break 1)
  call-interactively(gud-break nil nil)
  command-execute(gud-break)


  Thanks.