Bug 124629 Use Top/Bottom n in a field containing null value inside will cause DataException.
Description: Use Top/Bottom n in a field containing null value inside will cause DataException. Steps to reproduce: 1. New a data source and dataset 2. Add a filter on a field, set operator to top 5 3. Click Preview Result. Result: A BIRT exception occurred. Plug-in Provider:Eclipse.org Plug-in Name:BIRT Data Engine Plug-in ID:org.eclipse.birt.data Version:2.0.0 Error Code:data.engine.DataConversionError Error Message:An error happened in data type conversion. Can not convert the value of {NULL_VALUE_!@#$%^&} to Double type.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/script/NEvaluator.java
qualifiedRowCounter = 0;
		rowIdList = null;
		valueList = null;
		N = -1;
	}
	protected abstract Object doCompare( Object value1, Object value2 ) throws DataException;
}
/**
 * The class that provides "Top N" calculation service
 *
 */
class TopNEvaluator extends NEvaluator
{
	protected Object doCompare( Object value1, Object value2 ) throws DataException
	{
		return ScriptEvalUtil.evalConditionalExpr2( value1, IConditionalExpression.OP_GT, value2, null);
	}
}
/**
 * The class that provides "Bottom N" calculation service
 *
 */
class BottomNEvaluator extends NEvaluator
{
	protected Object doCompare( Object value1, Object value2 ) throws DataException
	{
		return ScriptEvalUtil.evalConditionalExpr2( value1, IConditionalExpression.OP_LT, value2, null);
	}
}