won't work with niconico video-titles - "Uncaught TypeError: Cannot call method 'getPropertyValue' of null"

What steps will reproduce the problem?
1. open any video on nicovideo.jp (when logged in), like e.g. 
http://www.nicovideo.jp/watch/sm10520468
2. hove over the video's title - no rikaikun popup, on devel-console the error 
"Uncaught TypeError: Cannot call method 'getPropertyValue' of null" is 
displayed in (rikaicontent.js 454)

What version of the product are you using? On what operating system?
0.8.1 with chromium 16.0.912.63 on linux

Please provide any additional information below.
Same behavior in the taglist below the video's description

title is in a <p> tag:

<p id="video_title"><!-- google_ad_section_start 
-->【初音ミク&amp;神威がくぽ】 ANT WARRIOR 
【オリジナル曲】<!-- google_ad_section_end --><a id="video_article" 
href="#" target="_blank"><img 
src="http://res.nimg.jp/img/common/icon/dic_off.png" alt="大百科"></a><a 
id="nicommons" href="" target="_blank" style="display: none;"><img 
src="http://res.nimg.jp/img/watch/tit_icon/commons.png" 
alt="コモンズ"></a></p>

Tags are also within a <p> with google_ad_section - so maybe related, maybe 
just coincidence.

Original issue reported on code.google.com by lohma...@googlemail.com on 6 Jan 2012 at 8:52

UraYukimitsu / rikaikun

won't work with niconico video-titles - "Uncaught TypeError: Cannot call method 'getPropertyValue' of null" #69