@Override
  public String toString() {
    if (dex == null) {
      return String.valueOf(offset);
    }
    return dex.protoIds().get(offset).toString();
  }
A call_site_id_item: https://source.android.com/devices/tech/dalvik/dex-format#call-site-id-item
android/android_framework/dex-maker/src/main/java/com/android/dex/CallSiteId.java