Bug 188843 NPE throws out when preview sample report in xls[1203]
engine/org.eclipse.birt.report.engine.emitter.prototype.excel/src/org/eclipse/birt/report/engine/emitter/excel/StyleEngine.java
* @param dataMap
	 *            layout data
	 * @return a StyleEngine instance
	 */
	public static StyleEngine createStyleEngine( ListBuffer dataMap )
	{
		engine.release( );
		engine.setDataMap( dataMap );
		return engine;
	}
	private StyleEngine( )
	{
	}
	public void addContainerStyle( IStyle style, Span span, int start )
	{
		StyleEntry entry = initStyle( style, span );
		spans.push( span );
		styles.push( entry );
		pos.push( new Integer( start ) );
		style2top.put( entry, Boolean.TRUE );
	}
	public void calculateTopStyles( )
	{
		if ( styles.size( ) > 0 )
		{
			StyleEntry style = (StyleEntry)styles.peek( );
			
			if(((Boolean)style2top.get( style )).booleanValue( )) 
			{	
				Span span = (Span) spans.peek( );