code: public MultiRuntimeConfigurationBuilder setDefaultRuntime(final String runtimeName) {
      Validate.isTrue(SUPPORTED_RUNTIMES.contains(runtimeName), "Unsupported runtime " + runtimeName);
      Validate.isTrue(!this.defaultRuntime.isPresent(), "Default runtime was already added");
  
      this.defaultRuntime = Optional.of(runtimeName);
      return this;
    }
docs: Sets default runtime. Default runtime is used when no runtime was specified for evaluator
  @param runtimeName the default runtime name
  @return The builder instance