@Nonnull
		@Override
		public String getExtension() {
			if (file != null) {
				return Util.extension(getFile().toString());
			} else {
				return ResourceRef.super.getExtension();
			}
		}
A <code>ResourceResolver</code> that, when given a resource string which
looks like a path to a file on the local file system, will return a reference
to that file.
src/main/java/dev/jbang/source/resolvers/FileResourceResolver.java