code: public Image get(ImageDescriptor descriptor) {
  		if (descriptor == null)
  			descriptor= ImageDescriptor.getMissingImageDescriptor();
  
  		Image result= (Image)fRegistry.get(descriptor);
  		if (result != null)
  			return result;
  
  		Assert.isTrue(fDisplay == SWTUtil.getStandardDisplay(), "Allocating image for wrong display."); //$NON-NLS-1$
  		result= descriptor.createImage();
  		if (result != null)
  			fRegistry.put(descriptor, result);
  		return result;
  	}
docs: Returns the image associated with the given image descriptor.
  
  @param descriptor the image descriptor for which the registry manages an image,
  or <code>null</code> for a missing image descriptor
  @return the image associated with the image descriptor or <code>null</code>
  if the image descriptor can't create the requested image.