Bug 193886 NPE is thrown when preview external CSS style in ppt[1205]
engine/org.eclipse.birt.report.engine.emitter.ppt/src/org/eclipse/birt/report/engine/emitter/ppt/PPTRender.java
else if ( content instanceof String )
			{
				imageURI = (String) content;
				generateImageBytes( imageURI );
			}
			pptOutput.write( "\n\n".getBytes( ) );
		}
		pptOutput.write( "</p:slide></body></html>\n".getBytes( ) ); 
	}
	private void exportImageHeader( String imagekey ) throws IOException
	{
		pptOutput.write( "\n".getBytes( ) );
		pptOutput.write( "--___Actuate_Content_Boundary___\n".getBytes( ) ); 
		pptOutput.write( ( "Content-Location: file:/C:/___Actuate___/"
				+ (String) imageNames.get( imagekey ) + "\n" ).getBytes( ) );
		pptOutput.write( "Content-Transfer-Encoding: base64\n".getBytes( ) );
		pptOutput.write( ( "Content-Type: image/"
				+ (String) imageExtensions.get( imagekey ) + "\n\n" ).getBytes( ) );
	}
	private void generateImageBytes( String imageURI ) throws IOException
	{
		exportImageHeader( imageURI );
		Base64 base = new Base64( );
		URL imageURL = null;
		if ( reportDesign != null )
		{
			imageURL = reportDesign.findResource( imageURI,
					IResourceLocator.IMAGE );
		}
		if ( imageURL.toString( ).toLowerCase( ).endsWith( ".svg" ) )