code: public boolean containsKey(Key<?> key) {
      for (int i = 0; i < size; i++) {
        if (bytesEqual(key.asciiName(), name(i))) {
          return true;
        }
      }
      return false;
    }
docs: Returns true if a value is defined for the given key.
  
  <p>This is done by linear search, so if it is followed by {@link #get} or {@link #getAll},
  prefer calling them directly and checking the return value against {@code null}.