This line does not compile with java6 (java7 compiles successfully). 

>/hazelcast/hazelcast/src/main/java/com/hazelcast/concurrent/atomicreference/proxy/AtomicReferenceProxy.java:[86,21] type parameters of <E>E cannot be determined; no unique maximal instance exists for type variable E with upper bounds boolean,java.lang.Object

This can be converted to 

````
Boolean result = invoke(operation,nodeEngine);
return result;
````