Bug 182284 Error message props up after previewing a report with a group on date type column
Use the attached rptdesign file preview Expected Result: Data is grouped without error message. Actual result: error message props up.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/group/GroupCalculatorFactory.java
/**
	 * 
	 * @param dataType
	 * @return
	 */
	private static boolean isNumber( int dataType )
	{
		return ( dataType == DataType.DECIMAL_TYPE
				|| dataType == DataType.DOUBLE_TYPE || dataType == DataType.INTEGER_TYPE );
	}
	/**
	 * 
	 * @param dataType
	 * @return
	 */
	private static boolean isDate( int dataType )
	{
		return ( dataType == DataType.DATE_TYPE );
	}
	/**
	 * 
	 * @param dataType
	 * @return
	 */
	private static boolean isString( int dataType )
	{
		return ( dataType == DataType.STRING_TYPE );
	}
}