[rules-users] ArrayList in Guvnor 5.1 M2

Hi All I have built the following rule in version 5.0 with no errors: rule "When average temperature is greater than 19" lock-on-active true when $t : ArrayList() from collect(Temperature()) //store all temperature objects in an arraylist $average: Number(doubleValue>19) from accumulate(Temperature($val:value),average($val)) //calculate the average temperature $f : ArrayList() from collect(Fan()) then System.out.println($average); turnOnFans($f); //function -> send arraylist of fan objects to function end but when i try to build in version 5.1 i get a java.lang.ArrayStoreException. Any help much appreciated. Kind regards, James.