code: public BUILDER setUndefinedMetricValue(ModelNode undefinedMetricValue) {
          this.undefinedMetricValue = (undefinedMetricValue == null || !undefinedMetricValue.isDefined()) ? null : undefinedMetricValue;
          return (BUILDER) this;
      }
docs: Sets a {@link AttributeDefinition#getUndefinedMetricValue()  default value} to use for the
  metric if no runtime value is available (e.g. we are a server running in admin-only mode).
  
  @param undefinedMetricValue the default value, or {@code null} if no default should be used
  @return a builder that can be used to continue building the attribute definition