private void ensureUnwalkablePolygonIsMutable() {
        if (!((bitField0_ & 0x00000010) == 0x00000010)) {
          unwalkablePolygon_ = new java.util.ArrayList<org.bwapi.proxy.messages.TerrainMessages.Polygon>(unwalkablePolygon_);
          bitField0_ |= 0x00000010;
         }
      }