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
*            the report content
	 */
	public void start( IReportContent rc )
	{
		report = rc;
		if ( !imageNames.isEmpty( ) )
		{
			imageNames.clear( );
		}
		if ( !fileNamesLists.isEmpty( ) )
		{
			fileNamesLists.clear( );
		}
		try
		{
			pptOutput.write( "MIME-Version: 1.0\n".getBytes( ) ); 
			pptOutput.write( "Content-Type: multipart/related; boundary=\"___Actuate_Content_Boundary___\"\n".getBytes( ) ); 
			pptOutput.write( "\n".getBytes( ) ); 
			pptOutput.write( "--___Actuate_Content_Boundary___\n".getBytes( ) ); 
			pptOutput.write( "Content-Location: file:/C:/___Actuate___/slide-show\n".getBytes( ) ); 
			pptOutput.write( "Content-Transfer-Encoding: quoted-printable\n".getBytes( ) ); 
			pptOutput.write( "Content-Type: text/html; charset=\"utf-8\"\n".getBytes( ) ); 
			pptOutput.write( "\n".getBytes( ) ); 
			pptOutput.write( "<html\n".getBytes( ) ); 
			pptOutput.write( "xmlns=3D'http:www.w3.org/TR/REC-html40'\n".getBytes( ) ); 
			pptOutput.write( "xmlns:o=3D'urn:schemas-microsoft-com:office:office'\n".getBytes( ) ); 
			pptOutput.write( "xmlns:p=3D'urn:schemas-microsoft-com:office:powerpoint'\n".getBytes( ) ); 
			pptOutput.write( "xmlns:v=3D'urn:schemas-microsoft-com:vml'\n".getBytes( ) ); 
			pptOutput.write( ">\n".getBytes( ) ); 
			pptOutput.write( "<head>\n".getBytes( ) );