lib/mail/Header.php
public function jsonSerialize()
    {
        return array_filter(
            [
                'key' => $this->getKey(),
                'value' => $this->getValue()
            ],
            function ($value) {
                return $value !== null;
            }
        ) ?: null;
    }
public function jsonSerialize()
    {
        return array_filter(
            [
                'key' => $this->getKey(),
                'value' => $this->getValue()
            ],
            function ($value) {
                return $value !== null;
            }
        ) ?: null;
    }
public function jsonSerialize ( ) { return array_filter ( [ 'key' => $ this -> getKey ( ) , 'value' => $ this -> getValue ( ) ] , function ( $ value ) { return $ value !== null ; } ) ? : null ; }
Return an array representing a Header object for the Twilio SendGrid API

@return null|array
Return an array representing a Header object for the Twilio SendGrid API