code: @SuppressWarnings("deprecation")
      public BUILDER addArbitraryDescriptor(String arbitraryDescriptor, ModelNode value) {
          if (this.arbitraryDescriptors == null) {
              this.arbitraryDescriptors = Collections.singletonMap(arbitraryDescriptor, value);
          } else {
              if (this.arbitraryDescriptors.size() == 1) {
                  this.arbitraryDescriptors = new HashMap<>(this.arbitraryDescriptors);
              }
              arbitraryDescriptors.put(arbitraryDescriptor, value);
          }
          return (BUILDER) this;
      }
docs: Adds {@link AttributeDefinition#getArbitraryDescriptors() arbitrary descriptor}.
  @param arbitraryDescriptor the arbitrary descriptor name.
  @param value the value of the arbitrary descriptor.
  @return a builder that can be used to continue building the attribute definition