Bug 118592 Report error
please see attached design file.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/ResultIterator.java
* A convenience method for the API consumer. <br>
	 * If the expression value has an incompatible type, a ClassCastException is
	 * thrown at runtime.
	 * 
	 * @param dataExpr
	 *            An IBaseExpression object provided in the ReportQueryDefn at
	 *            the time of prepare.
	 * @return The value of the given expression as a String. It could be null.
	 * @throws DataException
	 *             if error occurs in Data Engine
	 */
	public String getString( IBaseExpression dataExpr ) throws DataException
	{
		try
		{
			return DataTypeUtil.toString( getValue( dataExpr ) );
		}
		catch ( BirtException e )
		{
			DataException e1 = new DataException( ResourceConstants.DATATYPEUTIL_ERROR,
					e );
			logger.logp( Level.FINE,
					ResultIterator.class.getName( ),
					"getString",
					"An error is thrown by DataTypeUtil.",
					e1 );
			throw e1;
		}
	}
	/**