Symfony version(s) affected

4.4+

Description

When a default option is defined, it cannot be overridden by a null value in the $options parameter of the request method because of how HttpClientTrait::mergeDefaultOptions is working: using isset exclude every override with a null value.

I noticed the bug using the proxy option. In this case, passing false does disable the proxy, however the proxy option is expected to be a string or null so this is not really a good solution (and might cause issues with some implementations?)

How to reproduce

• Define a proxy in framework.http_client.default_options
• Try to disable the use of the proxy for a specific request by passing 'proxy' => null to the request options
• The default option proxy is still used.

(Can probably be reproduced with any other options handled by the same isset condition)

Possible Solution

Use !array_key_exists($k, $options) instead of !isset($options[$k].
The documentation says about the options:

They can be defined globally in the configuration (to apply it to all requests) and to each request (which overrides any global configuration).

So any key that exists in the $options array should override the default options, no matter the value.

Additional Context

No response