why currentIssue.getModifiedFields().size() always gives Zero

[ramesh_babu NA]

I am using Script runner and I edit through "Edit Screen" and calling Event Updated, I am getting "zero" for Current issue, irrespective of fields I change

MutableIssue currentIssue = (MutableIssue) event.getIssue();
log.debug( currentIssue.getKey());

Map<String,ModifiedValue> changes = currentIssue.getModifiedFields()
log.debug("Number of changes : " + changes?.size());
 
==Output
20150226 17.31.40 DEBUG [com.jira.groovy.listeners.FixVersionListener]: MYT-18

20150226 17.31.40 DEBUG [com.jira.groovy.listeners.FixVersionListener]: Number of changes : 0

[ramesh_babu NA]

got moodified fileds from https://answers.atlassian.com/questions/223177

OfBizDelegator delegator = ComponentAccessor.getOfBizDelegator()
 
GenericValue changelog = event.getChangeLog() 
Long changeGroupId = changelog.getLong("id")
 List<GenericValue> changeItems = delegator.findByAnd("ChangeItem",MapBuilder.build("group", changeGroupId));
log.info("****** number of changes: {}" + changeItems.size());
 






for (GenericValue changetemp:changeItems ){

				 log.debug( "*************** changetemp.getString(field):  " + changetemp.getString("field"));

				 log.debug( "*************** changetemp.getString(oldstring):  " + changetemp.getString("oldstring"));

				 log.debug( "*************** changetemp.getString(newstring):  " + changetemp.getString("newstring"));

				 

			 }