private URL getDefaultUrl() {
		return ResourceManager.getResource(ResourceManager.BOMB);
	}
Returns the value of {@link #getUrl()} if it is non-null.  Otherwise, this class will
attempt to create a temporary file containing the image of this class in order to return
a URL for that temp file.  If a temporary file could not be created, then the URL 
returned from this class will point to the 
{@link ResourceManager#getDefaultIcon() default icon}.

@return the URL
Ghidra/Framework/Gui/src/main/java/resources/IconProvider.java