public function getHeader($key)
    {
        foreach ($this->headers as $header => $content) {
            if (strtolower($key) === strtolower($header)) {
                return $content;
            }
        }
        return null;
    }
public function getHeader($key)
    {
        foreach ($this->headers as $header => $content) {
            if (strtolower($key) === strtolower($header)) {
                return $content;
            }
        }
        return null;
    }
public function getHeader ( $ key ) { foreach ( $ this -> headers as $ header => $ content ) { if ( strtolower ( $ key ) === strtolower ( $ header ) ) { return $ content ; } } return null ; }
Return header by key if it exists.

@param string $key

@return null|string
Return header by key if it exists .