code: public static Key JOIN_PROMPT(String value, Voice voice) {
  
        Map<String, String> map = new HashMap<String, String>();
        map.put("value", value);
        if (voice != null) {
          map.put("voice", voice.toString());
        }
  
        return createKey("joinPrompt", map);
      }
docs: Defines a prompt that plays to all participants of a conference when
  someone joins the conference.It's possible to define either TTS or an audio
  URL using additional attributes value and voice
  
  @param value
  value is used to play simple TTS and/or an audio URL, and supports
  SSML
  @param voice
  voice is used to define which of the available voices should be
  used for TTS; if voice is left undefined, the default voice will
  be used
  @return