There seem to be some logging confusions when the new mail templates has been configured for JIRA 4.4.

Here is the sample stack trace from the logs:

ERROR ServiceRunner    Mail Queue Service [velocity] RHS of #set statement is null.
Context will not be modified. templates/email/html/includes/fields/changelog.vm [line 26, column 1]

and line 26, column 1 of the changelog.vm file:

#set ($oldText = $velocityhelper.getPrettyFieldString($changeitem.getString("field"), $changeitem.getString($oldstringKey), $i18n))

So far, no critical problems were reported, but this stack trace should be handled appropriately.