Bug 135778 There is an error when the data item has no binding data set
Data item can have no binding data set, if it happens, it indicates it only use the basic Java Script function such as new Date(). At this moment, the data of data item is not stored in report document by DtE, which only supports these data items which has binding data set.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/executor/transform/group/GroupCalculationUtil.java
/**
	 * Sort data rows by group information and sort specification
	 * 
	 * @throws DataException
	 */
	public SortSpec getSortSpec( ) throws DataException
	{
		assert groupDefs != null;
		
		
		int groupCount = 0;
		int sortCount = 0;
		for ( int i = 0; i < groupDefs.length; i++ )
		{
			
			
			if ( groupDefs[i].getColumnIndex( ) >= 0 )
			{
				groupCount++;
			}
		}
		if ( query.getOrdering( ) != null )
		{
			sortCount = query.getOrdering( ).length;
		}
		int[] sortKeyIndexes = new int[groupCount + sortCount];
		String[] sortKeyColumns = new String[groupCount + sortCount];
		boolean[] sortAscending = new boolean[groupCount + sortCount];
		for ( int i = 0; i < groupCount; i++ )
		{