code: public void setSelfMuted(long userId, boolean muted) {
          if (muted) {
              selfMuted.add(userId);
          } else {
              selfMuted.remove(userId);
          }
      }
docs: Sets the self-muted state of the user with the given id.
  
  @param userId The id of the user.
  @param muted Whether the user with the given id is self-muted or not.