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
FloatValue positionValX = (FloatValue) containerStyle.getProperty( StyleConstants.STYLE_BACKGROUND_POSITION_X );
		FloatValue positionValY = (FloatValue) containerStyle.getProperty( StyleConstants.STYLE_BACKGROUND_POSITION_Y );
		if ( positionValX == null || positionValY == null )
		{
			return;
		}
		boolean xMode, yMode;
		double positionX, positionY;
		if ( positionValX.getPrimitiveType( ) == CSSPrimitiveValue.CSS_PERCENTAGE )
		{
			positionX = PropertyUtil.getPercentageValue( positionValX );
			xMode = true;
		}
		else
		{
			positionX = pptMeasure( PropertyUtil.getDimensionValue( positionValX ) );
			xMode = false;
		}
		if ( positionValY.getPrimitiveType( ) == CSSPrimitiveValue.CSS_PERCENTAGE )
		{
			positionY = PropertyUtil.getPercentageValue( positionValY );
			yMode = true;
		}
		else
		{
			positionY = pptMeasure( PropertyUtil.getDimensionValue( positionValY ) );
			yMode = false;
		}
		drawBackgroundImage( bi,
				startX,