Initialize Client\Response::$reasonPhrase - #19577

Fixes #19576.

Cake\Http\Client\Response::$reasonPhrase is assigned in only two places: _parseHeaders(), when a header line matches an HTTP/x.y NNN status line, and withStatus(). Construct a response without a status line and neither runs, so the property stays uninitialized:

$response = new Cake\Http\Client\Response([], 'Okay body.');
$response->getReasonPhrase();
// Error: Typed property Cake\Http\Client\Response::$reasonPhrase
//        must not be accessed before initialization

A method declared : string should not fatal, and PSR-7 requires getReasonPhrase() to return a string.

Defaulting the property to '' is what PSR-7 allows when no reason phrase is known, and matches the reporter's suggestion.

Not a 5.x regression

Worth noting for triage: this is not new. 52104f3 ("Add native type hints for Http properties") changed protected $reasonPhrase; to protected string $reasonPhrase;, but getReasonPhrase(): string already carried the string return type before that commit. So the untyped default was null and the same call raised TypeError: Return value must be of type string, null returned. The typed property only changed the error message.

Left out on purpose

The related inconsistency in the issue thread is not addressed here, since it is a behavior change rather than a fix:

Http\Response::_setStatus() fills an empty reason phrase from its $_statusCodes map; the client class has no such map and stores whatever it is given. Making the two consistent would change output for existing withStatus() callers, so it seems better suited to 5.next if wanted at all. Happy to follow up.