[rules-users] Accumulate function, events and stream processing

I need your help to put to work an accumulate function. So, i will introduce several facts into working memory (StateEvent, which i declare as event) and i want to accumulate the last five values. I have changed a property in drools.default.rulebase.conf (drools.eventProcessingMode = STREAM) to make the engine works in stream mode. And my rule is: declare StateEvent @role( event ) end rule "Testing" when $total : Number() from accumulate( StateEvent(itemName=="Temperatura", $val : newState) over window:length( 5 ), sum ( ((DecimalType)$val).toBigDecimal().doubleValue() ) ) then #actions end But it's not working, as the value of $total is 0.0, no matter what i do, and the rule is firing with every fact in the working memory. Any help will be appreciated. Thanks