@Override
  public boolean containsKey(Object o) {
    if (o instanceof char[] text) {
        return containsKey(text, 0, text.length);
    } 
    return containsKey(o.toString());
  }
true if the <code>CharSequence</code> is in the {@link #keySet()}
linguistics/src/main/java/com/yahoo/language/simple/kstem/CharArrayMap.java