ImageDescriptor exception in RCP Application

I am a newbie to EclipseRCP and I am trying to get a product from EclipseRCP. In my program, I am loading some images(flags for language switches etc.). I am trying to load them in this way:

Image favcon= AbstractUIPlugin.imageDescriptorFromPlugin("HelloRCP", 
                  "images/configuration.jpg").createImage(display);

There are also some other place that I use this code snippet (I am defining a new Image instance at that time). I got a Null pointer exception at th开发者_开发问答at second usage of image descriptor. What can be reason for this situation ?

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Are the images in images in the root directory?

Try using "/images/configuration.jpg" instead of "images/configuration.jpg"