Solves an issue where issue has no attribute

ERROR 2014-08-28T10:55:02 Uncaught exception in _callRegexp:
Traceback (most recent call last):
  File "/usr/lib/pymodules/python2.7/supybot/callbacks.py", line 1356, in _callRegexp
    method(irc, msg, m)
  File "/home/bolek/.supybot/plugins/Jira/plugin.py", line 82, in getIssue
    if issue.fields.assignee:
AttributeError: type object 'PropertyHolder' has no attribute 'assignee'

This may happen when bot user in Jira has no access to some attributes like assignee or timeestimate.