code: public List<String> getServiceImplementations(String serviceTypeName) {
          final List<String> strings = services.get(serviceTypeName);
          return strings == null ? Collections.<String>emptyList() : Collections.unmodifiableList(strings);
      }
docs: Get the service implementations for a given type name.
  
  @param serviceTypeName the type name
  @return the possibly empty list of services