src/Config/Argument.php
public function required() {
        $this->validated = false;
        $this->config[self::REQUIRED] = true;
        return $this;
    }
public function required() {
        $this->validated = false;
        $this->config[self::REQUIRED] = true;
        return $this;
    }
public function required ( ) { $ this -> validated = false ; $ this -> config [ self :: REQUIRED ] = true ; return $ this ; }
change the argument from optional to mandatory

@return $this
change the argument from optional to mandatory