code: public RuntimeEnvironmentBuilder entityManagerFactory(Object emf) {
          if (emf == null) {
              return this;
          }
          if (!(emf instanceof EntityManagerFactory)) {
              throw new IllegalArgumentException("Argument is not of type EntityManagerFactory");
          }
          _runtimeEnvironment.setEmf((EntityManagerFactory)emf);
  
          return this;
      }
docs: Sets entityManagerFactory.
  
  @param emf entityManagerFactory
  @return this RuntimeEnvironmentBuilder