public Builder clearUnwalkablePolygon() {
        if (unwalkablePolygonBuilder_ == null) {
          unwalkablePolygon_ = java.util.Collections.emptyList();
          bitField0_ = (bitField0_ & ~0x00000010);
          onChanged();
        } else {
          unwalkablePolygonBuilder_.clear();
        }
        return this;
      }