code: private Multimap<Type, Class<?>> filterProducibleClasses(Map<Key<?>, Class<?>> bindings) {
          Multimap<Type, Class<?>> defaultFactoryToBind = ArrayListMultimap.create();
          bindings.entrySet()
                  .stream()
                  .filter(entry -> isCandidate(entry.getKey()
                          .getTypeLiteral()
                          .getType()))
                  .forEach(entry -> defaultFactoryToBind.put(entry.getKey()
                          .getTypeLiteral()
                          .getType(), entry.getValue()));
          return defaultFactoryToBind;
      }
docs: Filter a map containing pairs of interface/implementation in order to get only producible
  classes.
  
  @param bindings map of interface/implementation
  @return producible pairs