default long[] multiGet(long[] key) {
    long[] result = new long[key.length];
    for (int i = 0; i < key.length; i++) {
      result[i] = get(key[i]);
    }
    return result;
  }
Returns the value for {@code key}. Safe to be called by multiple threads after all values have been written. After
the first read, all writes will fail.
planetiler-core/src/main/java/com/onthegomap/planetiler/collection/LongLongMap.java