code: public static <T> T resolveMandatory(Class<T> c) {
      T obj = resolve(c);
      if (obj == null) {
        Error err = new LinkageError("No implementation found for: " + c.getName());
        throw err;
      }
      return obj;
    }
docs: Return a provider for this interface.
  
  @param c the provider interface that is implemented
  @param <T> type of provider interface
  
  @return instance of the provider, never null
  @throws java.lang.LinkageError if there is a problem instantiating the provider
  or no provider was specified