Bug 164764 Joint data set does not work properly using attached flatfile
The data set preview keep empty in joint data set. Step to reproduce: 1.Create two data sets based on attached flat file 2.Make an inner join using joint data set with key "A". 3.Preview data set in data set editor. Expect result: The data set preview correctly Actual result: The data set preview is empty.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/script/ScriptEvalUtil.java
* @param result
		 * @return
		 */
		private static boolean isDateOrString( Object result )
		{
			return ( result instanceof Date ) || ( result instanceof String );
		}
		/**
		 * To check whether the expressions are comparable. If so, they will be
		 * formatted to the comparable.For operands, only ExprTextAndValue is
		 * acceptable.
		 * 
		 * @param obj
		 * @param operator
		 * @param op1
		 * @param op2
		 * @return
		 * @throws DataException
		 */
		private static Object[] isComparable( Object obj, int operator,
				ExprTextAndValue op1, ExprTextAndValue op2 )
				throws DataException
		{
			if ( needFormat( obj, operator, op1, op2 ) )
				return formatToComparable( obj, op1, op2 );
			return null;
		}
		/**
		 * 
		 * @param obj