src/HttpHandler.php
public function hasHeader(string $key = null) : bool
	{
		if ($key === null) {
			return false;
		}

		$array = $this->getHeaders();
		return isset($array[$key]) || array_key_exists($key, $array);
	}
public function hasHeader(string $key = null) : bool
	{
		if ($key === null) {
			return false;
		}

		$array = $this->getHeaders();
		return isset($array[$key]) || array_key_exists($key, $array);
	}
public function hasHeader ( string $ key = null ) : bool { if ( $ key === null ) { return false ; } $ array = $ this -> getHeaders ( ) ; return isset ( $ array [ $ key ] ) || array_key_exists ( $ key , $ array ) ; }
Returns whether a header exists or not.

@param  string|null $key The header key.
@return bool
Returns whether a header exists or not .