It seems that headerNames would never be null
@@ -29,8 +29,8 @@ class Message implements MessageInterface, Stringable
/** @var array<string, array<string>> */
protected array $headers = [];
- /** @var array<string>|null */
- protected ?array $headerNames = null;
+ /** @var array<string> */
+ protected array $headerNames = [];
protected bool $keepAlive = true;
