log.setLevel(org.apache.log4j.Level.DEBUG);
MutableIssue issue = issue;
CustomField cfQAContact = ComponentAccessor.getCustomFieldManager().getCustomFieldObjectByName("QA Contact");
def qacontact = issue.getCustomFieldValue(cfQAContact);
if(qacontact==null)
{
def currentReporter = issue.reporter;
issue.setCustomFieldValue(cfQAContact, currentReporter);
issue.store();
}