docs: public ModifiableHyperBoundingBox computeMBR() {
      E firstEntry = getEntry(0);
      if(firstEntry == null) {
        return null;
      }
      // Note: we deliberately get a cloned copy here, since we will modify it.
      ModifiableHyperBoundingBox mbr = new ModifiableHyperBoundingBox(firstEntry);
      for(int i = 1; i < numEntries; i++) {
        mbr.extend(getEntry(i));
      }
      return mbr;
    }