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