Can't access settings before editing card

I installed Anki and started it up for the first time. I installed the SyntaxHighlight add-on using the code and restarted as instructed.

Then when I went to Tools -> Syntax Highlighting (options), I got the following exception:

An error occurred in an add-on. Please contact the add-on author.

Traceback (most recent call last):
  File "/home/user/Anki/addons/code_highlight_addon/code_highlight_addon.py", line 117, in setupUi
    if mw.col.conf['syntax_highlighting_conf']['linenos']:
KeyError: 'syntax_highlighting_conf'

Then I started adding a card to the default deck (which was empty). I saw that the addon was working. I cancelled saving the card and went back to its settings dialog. And it appeared okay (Line numbers: Switch on/off).