code: public MultiRuntimeDefinitionBuilder setDefaultRuntimeName(final String runtimeName){
      Validate.isTrue(StringUtils.isNotBlank(runtimeName),
              "runtimeName should be non empty and non blank string");
      this.defaultRuntime = runtimeName;
      return this;
    }
docs: Sets default runtime name.
  @param runtimeName The name of the default runtime
  @return The builder instance