Http/Response.php
public function getHeader($key)
    {
        return isset($this->_headers[$key]) ? $this->_headers[$key] : null;
    }
public function getHeader($key)
    {
        return isset($this->_headers[$key]) ? $this->_headers[$key] : null;
    }
public function getHeader ( $ key ) { return isset ( $ this -> _headers [ $ key ] ) ? $ this -> _headers [ $ key ] : null ; }
Returns the value of the requested header or null if it does not exist.

@param string $key
@return mixed|null
Returns the value of the requested header or null if it does not exist .