Bug 201017 TopN, TopPercent, BottomPercent filters will lead NPE when the values contains NULL[07]
data/org.eclipse.birt.data.tests/test/org/eclipse/birt/data/engine/aggregation/TotalTest.java
ac.start();
        ac.onRow(new Object[]{new Double(1), new Double(1)});
        ac.onRow(new Object[]{new Double(2), new Double(2)});
        ac.finish();
        System.out.println(ac.getValue( ));
        assertEquals(new Double(1.6666666666666667), ac.getValue());
        
        ac.start();
        ac.onRow(new Object[]{null, new Double(3)});
        ac.onRow(new Object[]{new Double(2), new Double(2)});
        ac.onRow(new Object[]{new Double(2), null});
        ac.finish();
        System.out.println(ac.getValue( ));
        assertEquals(new Double(2), ac.getValue());
        
        ac.start();
        ac.onRow(new Object[]{new Double(1), new Double(3)});
        ac.onRow(new Object[]{new Double(1), new Double(-3)});
        ac.finish();
        System.out.println(ac.getValue( ));
        assertEquals(null, ac.getValue());
        
        ac.start();
        ac.onRow(new Object[]{new Double(1), new Double(2)});
        ac.onRow(new Object[]{new Double(2), new Double(-4)});
        ac.finish();
        System.out.println(ac.getValue( ));
        assertEquals(new Double(3.0), ac.getValue());
        
        ac.start();