Wrong type argument: arrayp, nil

[Gracjan Polak <gracjanpolak@gmail.com>]

Hi,

I'm not sure if this is the correct place, I suspect it is not so please
forward me where to go.

So I was happily hacking on something totally other when my language
indentation mode after a TAB responded with friendly: Wrong type argument:
arrayp, nil.

Being ambitious programmer as I am I decided to debug the issue in the
indentation package that I use.

I have zero experience hacking emacs although I had used it for years now.

Here are steps I took:

Downloaded source code of package in question.

Looked up how to use some kind of debugging under emacs, found Edebug (not
sure if I found right).

Used C-u C-M-x to instrument main entry the function that got set in var
indent-line-function.

Added a friendly (please-break-here) so i know edebug got hooked properly.

Pressed TAB to indent...

Nothing happened.

Is there a how-to-debug-elisp tutorial somewhere? Currently I have no idea
how to setup my environment.

Where do I proceed?

-- 
Gracjan