I reproduced this issue in a very easy way as it follows:

    public static class person {
        private address address;

        public Misc2Test.address getAddress() {
            return address;
        }

        public void setAddress( Misc2Test.address address ) {
            this.address = address;
        }
    }

    public static class address { }

    @Test
    public void testLowerCaseClass() {
        // DROOLS-1015
        String drl =
                "import " + person.class.getCanonicalName() + "\n" +
                "import " + address.class.getCanonicalName() + "\n" +
                "global java.util.List list;\n" +
                "rule R when\n" +
                "    person( address == null )\n" +
                "then\n" +
                "    list.add(\"ok\");\n" +
                "end\n";

        KieSession ksession = new KieHelper().addContent( drl, ResourceType.DRL )
                                             .build()
                                             .newKieSession();

        List<String> list = new ArrayList<String>();
        ksession.setGlobal( "list", list );

        ksession.insert( new person() );
        ksession.fireAllRules();

        assertEquals( 1, list.size() );
    }

The problem here is caused by mvel class literals. In practice since 'address' is also the name of an imported class mvel interprets the constraint:

person( address == null )

as it was

person( address.class == null )

That of course always evaluates to false regardless if the person has a value in its address field or not. I'm trying to fix this problem without breaking this mvel feature by changing the precedence in which mvel disambiguate the 'address' word during parsing giving a lower priority to class literals. The problem is that at the moment all literals (like constants and even class literals) are the very first thing that are resolved by mvel during the parsing of an expression. I spent a couple of hours try to change this only for class literals, but the more I try the more I realize that achieving this result could take me many days of work.

I believe that going further with this attempt doesn't worth the effort for at least 2 good reason:

1. as you know one of the goal for drools 7 is getting rid of mvel.

2. there's an easy way to disambiguate the 'address' token. In fact replacing

person( address == null )

with

person( this.address == null )

will have the expected behavior.

My expectation is that the workaround I'm suggesting in 2. will also work for your use case.
This issue will be fixed in Drools 7.

Mario Fusco <mario.fusco> updated the status of jira DROOLS-1015 to Closed