Reported by Thomas:
============================
I've just tried upgrading from Drools 5.3.0-CR1 from the beta and I've hit a regression.

JBoss seems to have been down for most of today so I haven't been able to raise a Jira for it.

In our model we have Facts which contain fields of java.lang.class, we then have a rule which checks that they aren't null.
Eg
Fact

{ Class<Object> classField}

Rule "xyz"
When
Fact(classField != null)
Then
...
End

This is giving the following exception

Caused by: java.lang.ClassCastException: org.drools.base.field.ObjectFieldImpl cannot be cast to org.drools.base.field.ClassFieldImpl
at org.drools.base.evaluators.EqualityEvaluatorsDefinition$ClassEqualEvaluator.evaluate(EqualityEvaluatorsDefinition.java:1772)
at org.drools.rule.LiteralRestriction.isAllowed(LiteralRestriction.java:87)
at org.drools.rule.LiteralConstraint.isAllowed(LiteralConstraint.java:109)
at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:130)
at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:451)
at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:369)
at org.drools.reteoo.AlphaNode.assertObject(AlphaNode.java:134)
at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:451)
at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:379)
at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:204)
at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:244)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:330)
at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:291)
at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:882)
at org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:180)
... 149 more

Wrapping the classField != null within an eval appears to be a work around.

This is in the suspect method:
public boolean evaluate(InternalWorkingMemory workingMemory,
final InternalReadAccessor extractor,
final Object object1, final FieldValue object2) {
Object value1 = extractor.getValue( workingMemory, object1 );
Object value2 = object2.getValue();
if ( value2 == null )

{ ClassFieldImpl classField = (ClassFieldImpl) object2; value2 = classField.resolve( workingMemory ); }

return comparator.equals( value1, value2 );
}

I think the if statement just needs an instanceof check as well or some other way to track the fact that null may be a valid value to be comparing with!