docs: public final TypeAdapter<T> nullSafe() {
      return new TypeAdapter<T>() {
        @Override public void write(JsonWriter out, T value) throws IOException {
          if (value == null) {
            out.nullValue();
          } else {
            TypeAdapter.this.write(out, value);
          }
        }
        @Override public T read(JsonReader reader) throws IOException {
          if (reader.peek() == JsonToken.NULL) {
            reader.nextNull();
            return null;
          }
          return TypeAdapter.this.read(reader);
        }
      };
    }