code: @CheckReturnValue
      public GuildManager setRequiredMFALevel(Guild.MFALevel level)
      {
          Checks.notNull(level, "Level");
          Checks.check(level != Guild.MFALevel.UNKNOWN, "Level must not be UNKNOWN");
          this.mfaLevel = level.getKey();
          set |= MFA_LEVEL;
          return this;
      }
docs: Sets the {@link net.dv8tion.jda.core.entities.Guild.MFALevel MFA Level} of this {@link net.dv8tion.jda.core.entities.Guild Guild}.
  
  @param  level
  The new MFA Level for this {@link net.dv8tion.jda.core.entities.Guild Guild}
  
  @throws IllegalArgumentException
  If the provided level is {@code null} or UNKNOWN
  
  @return GuildManager for chaining convenience