Hi, I have a Map object that maps User product type experience with the level of expertise. I am trying to use accumulate in my rule Such that if the user has experience with certain product then it gets the experience level and sums it up . I am using Drools 5.1 , mvel 2, spring batch 2.x. This is my rule :- rule "Insert Product Types" dialect "mvel" salience 1800 when eval (true) then ProductType p1 = new ProductType(); p1.setName("P1"); ProductType p2 = new ProductType(); p2.setName("P2"); insert (p1); insert (p2); end rule "Product Class Experience" dialect "mvel" salience 1600 when ProductType ($name : name) $total : Number () from accumulate ( Client (productExperience.keySet contains $name, $score : productExperience[$name]), sum($score)) then System.out.println ("Product Type Score " + $total); End When the rule is fired I get the attached exception . Any suggestions / help will be great. Regards, Akash -------------------------------------------------------------------------- NOTICE: If you have received this communication in error, please destroy all electronic and paper copies and notify the sender immediately. Mistransmission is not intended to waive confidentiality or privilege. Morgan Stanley reserves the right, to the extent permitted under applicable law, to monitor electronic communications. This message is subject to terms available at the following link: http://www.morganstanley.com/disclaimers. If you cannot access these links, please notify us by reply message and we will send the contents to you. By messaging with Morgan Stanley you consent to the foregoing.