This is not the right fix for the issue. For instance, ->attributes is perfectly allowed to hold other types (for instance booleans) and that would be a BC break.

The right fix must be implemented in the conversion layer between BrowserKit and HttpFoundation, for the query and request parameters only.

Do you mean here?

I can put the casting right before the switch/case

No. This place is still in the HttpFoundation request object itself (which might add overhead the handling of actual web requests btw).

This should either be done when creating the BrowserKit request (might make sense as other BrowserKit implementations would also not be able to submit non-string values), or when converting from one to the other in

It would make most sense to put it in BrowserKit\Request then.

Thank you @rgeraads.

Am I just wondering in addition to fix the "null" issue (that is good), why this modified behavior for parameters I passed as POST request?

Input request parameters
array:8 [
"profileId" => 1000
]

After
array_walk_recursive($parameters, static function (&$value) {
$value = (string) $value;
});

array:8 [
"profileId" => "1000"
]

Input validation for request
/**
* @Assert\Type(type="integer")
* @Assert\NotNull
*/

Response:
Error: profileId should be "int"

Am I just wondering in addition to fix the "null" issue (that is good), why this modified behavior for parameters I passed as POST request?

And answer to my own question (for anyone who had the same issue) is not using "params" here that used for application/x-www-form-urlencoded, but using a body with JSON encoded parameters and a proper header.

Before:

        $this->client->request(
            'POST',
            $uri,
            $parameters,
            [],
            array_merge(['HTTP_AUTHORIZATION' => sprintf('Bearer %s', $this->jwtToken)], $headers)
        );

After:

        $this->client->request(
            'POST',
            $uri,
            [],
            [],
            array_merge(
                ['HTTP_AUTHORIZATION' => sprintf('Bearer %s', $this->jwtToken), 'CONTENT_TYPE' => 'application/json'],
                $headers
            ),
            json_encode($parameters, JSON_THROW_ON_ERROR)
        );