public function tier($tier = null)
    {
        if (is_null($tier)) {
            return $this->tier;
        }

        $this->tier = $tier;

        return $this;
    }
public function tier($tier = null)
    {
        if (is_null($tier)) {
            return $this->tier;
        }

        $this->tier = $tier;

        return $this;
    }
public function tier ( $ tier = null ) { if ( is_null ( $ tier ) ) { return $ this -> tier ; } $ this -> tier = $ tier ; return $ this ; }
Set the "tier" of the plan.

@param  string  $tier
@return $this
Set the tier of the plan .