Bug 212375 [Automation][Regression]Exception occurs when preview a outputParams["xxx"]
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/PreparedDataSourceQuery.java
/**
	 * 
	 * @return
	 */
	protected DataSetCacheManager getDataSetCacheManager( )
	{
		return this.dataEngine.getSession( ).getDataSetCacheManager( );
	}
	
	/**
	 * @return the appropriate subclass of the Executor
	 */
	protected abstract QueryExecutor newExecutor( );
	
	/*
	 * @see org.eclipse.birt.data.engine.impl.IPreparedQueryService#execSubquery(org.eclipse.birt.data.engine.odi.IResultIterator,
	 *      java.lang.String, org.mozilla.javascript.Scriptable)
	 */
	public IQueryResults execSubquery( IResultIterator iterator, IQueryExecutor parentExecutor,
			String subQueryName, Scriptable subScope ) throws DataException
	{
		return this.preparedQuery.execSubquery( iterator, parentExecutor,
				subQueryName,
				subScope );
	}
	
	/**
	 * 
	 */
	abstract class DSQueryExecutor extends QueryExecutor