NullPointerException when search engine robot tries to view IssueNavigator

The following NullPointerException might appear in logs:

2010-01-20 01:18:24,494 http-8090-Processor13 ERROR anonymous 4704x25290x1 s79le
http://issues.costrategix.net/secure/IssueNavigator.jspa [500ErrorPage.jsp] Exception caught in 500 page null
java.lang.NullPointerException
at com.atlassian.jira.util.BrowserUtils.getModifierKey(BrowserUtils.java:43)

It appears to be caused by search engine robots trying to access the IssueNavigator - the "browser" is unknown to the code and thus is null:

if (browser.getBrowserMajorVersion().compareTo(FIREFOX2) < 0)