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/impl/PreparedDataSourceQuery.java
public PreparedDataSourceQuery getDataSourceQuery( )
	{
		return this;
	}
	
	/**
	 * Executes the prepared execution plan.  This returns
	 * a QueryResult object at a state ready to return its 
	 * current result iterator, or evaluate an aggregate expression.
	 * <p>
	 * This includes setup runtime state, and evaluation of
	 * any beforeOpen and afterOpen scripts on a data set. 
	 * @return The QueryResults object opened and ready to return
	 * 		the results of a report query. 
	 */
	public IQueryResults execute( Scriptable scope ) throws DataException
	{
		return this.execute( null, scope );
	}
	/**
	 * Executes the prepared execution plan as an inner query that appears
	 * within the scope of another report query. The outer query must have been
	 * prepared and executed, and its results given as a parameter to this
	 * method.
	 * 
	 * @param outerResults
	 *            QueryResults for the executed outer query
	 * @return The QueryResults object opened and ready to return the results of
	 *         a report query.
	 */