code: private Class findServiceClass(Object service) {
          for (Class sc : _serviceProviders.keySet()) {
              if (sc.isInstance(service)) {
                  return sc;
              }
          }
          throw new IllegalArgumentException("Cannot find service provider for: " + service.getClass().getCanonicalName());
      }
docs: Try to find the registered service for a service object instance.
  May return null if the object instance is not from a service registered
  with this service provider.
  
  @return Service class for service instance.
  @throws IllegalArgumentException if service class can not be found.