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 );
			
			int rowBytes = saveExprValue( valueMap );
			IOUtil.writeLong( this.rowLenDos, currentOffset );
			currentOffset += rowBytes;
			lastRowIndex = currIndex;
		}
		catch ( IOException e )
		{
			throw new DataException( ResourceConstants.RD_SAVE_ERROR,
					e,
					"Result Data" );
		}
	}
	
	private int initSave( Map valueMap ) throws DataException
	{
		ByteArrayOutputStream tempBaos = new ByteArrayOutputStream( );
		BufferedOutputStream tempBos = new BufferedOutputStream( tempBaos );
		DataOutputStream tempDos = new DataOutputStream( tempBos );
		try
		{
			IOUtil.writeInt( tempDos, exprNameSet.size( ) );
			Iterator it = exprNameSet.iterator( );
			while ( it.hasNext( ) )
			{
				Object key = it.next( );
				IOUtil.writeObject( tempDos, key );
			}