public Phrase putOptional(String key, CharSequence value) {
    return keys.contains(key) ? put(key, value) : this;
  }
public Phrase putOptional ( String key , CharSequence value ) { return keys . contains ( key ) ? put ( key , value ) : this ; }
Silently ignored if the key is not in the pattern.

@see #put(String, CharSequence)