Drools condition cannot retrieve object from Map with Enum key

A fact : public class Convention { private Map<ECommissionType, List<Commission>> commissions = new HashMap<>(); } An enumeration : public enum ECommissionType { ACQ,RIS,POF,[...] } And a rule condition assuming $convention is properly initialized in a former condition and is an instance of the Convention class shown) : $comm : Commission() from $convention.getCommissions().get(ECommissionType.$1) Compilation using kie-maven-plugin is raising an error : Unable to Analyse Expression $convention.getCommissions().get(ECommissionType.RIS)): sun.reflect.generics.reflectiveObjects.ParameterizedTypeImpl cannot be cast to java.lang. Class : [Rule name= 'B_CommissionLigne_98' ]

As proposed on the stackoverflow topic, this works : rule comms when $conv: Convention() $comm: Comm() from (ArrayList)($conv.getComms()).get(Type.AAA) then [...] Please note the difference is an ArrayList cast (with a few parentheses).