code: public Datatype.Builder addValueTypeAnnotations(Excerpt element) {
      if (valueTypeAnnotations instanceof ImmutableList) {
        valueTypeAnnotations = new ArrayList<>(valueTypeAnnotations);
      }
      valueTypeAnnotations.add(Objects.requireNonNull(element));
      return (Datatype.Builder) this;
    }
docs: Adds {@code element} to the list to be returned from {@link
  Datatype#getValueTypeAnnotations()}.
  
  @return this {@code Builder} object
  @throws NullPointerException if {@code element} is null