code: public Optional<Field> resolveField(Class<?> someClass) {
          return Classes.from(someClass)
                  .traversingSuperclasses()
                  .fields()
                  .filter(elementAnnotatedWith(Identity.class, true))
                  .findFirst();
      }
docs: Resolves the first field holding annotated or meta-annotated with {@link Identity}.
  
  @param someClass the class to search for identity field.
  @return the {@link Field} wrapped in an {@link Optional}.