m.name = "IsNullOperator";
final FactPattern pat = new FactPattern( "Person" );
final SingleFieldConstraint con = new SingleFieldConstraint();
con.setFieldName( "age" );
con.setOperator( "== null" );
pat.addConstraint( con );
m.addLhsItem( pat );
String s = BRDRLPersistence.getInstance().marshal( m );
assertTrue( s.indexOf( "Person( age == null )" ) != -1 );