Bug 204229 [Automation][Regression]Exception is thrown when preview reportdesign in webviewer
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/document/RowSaveUtil.java
saveNullRowsBetween( lastRowIndex, currIndex );
			rowExprsDos.close( );
			rowLenDos.close( );
		}
		catch ( IOException e )
		{
			throw new DataException( ResourceConstants.RD_SAVE_ERROR,
					e,
					"Result Data" );
		}
	}
	/**
	 * init save environment
	 */
	private void initSave( boolean finish ) throws DataException
	{
		if ( inited == true )
			return;
		inited = true;
		try
		{
			
			IOUtil.writeInt( this.rowExprsDos, rowCount );
			
			Map map = new HashMap();
			Iterator it = exprNameSet.iterator( );
			while(it.hasNext( ))
			{
				Object value = it.next( );
				map.put( value, value );