class MutableSpan implements Cloneable {

  @Nullable public String tag(String key) {
    if (key == null) throw new NullPointerException("key == null");
    if (key.isEmpty()) throw new IllegalArgumentException("key is empty");
    for (int i = 0, length = tagCount * 2; i < length; i += 2) {
      if (key.equals(tags[i])) return (String) tags[i + 1];
    }
    return null;
  }

  public  MutableSpan();
  public  MutableSpan(TraceContext context, @Nullable MutableSpan defaults);
  public  MutableSpan(MutableSpan toCopy);

}