Sorry I'm not quire sure I'm following your errors... Are you saying you are having null pointer exceptions with this version: global List list rule "count from global List - but don't do it" when Number( $i: intValue ) from accumulate( Person( age > 20 ) from list, count(1) ) then System.out.println( $i + " Persons" ); end -- View this message in context: http://drools.46999.n3.nabble.com/Drools-and-ArrayList-tp3140821p3158948.... Sent from the Drools: User forum mailing list archive at Nabble.com.