@Test
 public void test_toString() {
   assertEquals("foo", converter.toString("foo"));
   assertEquals("foo.bar", converter.toString("foo.bar"));
   // conflict with Spray keyword
   assertEquals("foo.^custom.bar", converter.toString("foo.custom.bar"));
 }
 @Test
 public void test_toValue() {
   assertEquals("foo", converter.toValue("foo", null));
 }