public Builder addField(
          int index, com.google.protobuf.DescriptorProtos.FieldDescriptorProto value) {
        if (fieldBuilder_ == null) {
          if (value == null) {
            throw new NullPointerException();
          }
          ensureFieldIsMutable();
          field_.add(index, value);
          onChanged();
        } else {
          fieldBuilder_.addMessage(index, value);
        }
        return this;
      }