public static String getExtension(final URI file) {
        return file == null ? null : getExtension(file.toString());
    }
@Test
    void shouldGetExtension() {
        assertThat(FileUtils.getExtension((String)null), nullValue());
        assertThat(FileUtils.getExtension(""), nullValue());
        assertThat(FileUtils.getExtension("/file/hello"), nullValue());
        assertThat(FileUtils.getExtension("/file/hello.txt"), is(".txt"));
    }