public Builder addNormals(
          int index, org.box2d.proto.Box2D.PbVec2 value) {
        if (normalsBuilder_ == null) {
          if (value == null) {
            throw new NullPointerException();
          }
          ensureNormalsIsMutable();
          normals_.add(index, value);
          onChanged();
        } else {
          normalsBuilder_.addMessage(index, value);
        }
        return this;
      }