The constructor parameter $expires of the Cookie class is typed as string|null. That is surprising because that parameter is expected to be provided as a Unix timestamp which is usually an integer. Also, looking at the tests and the documentation, we commonly call that constructor with an integer ourselves, usually with a value returned by strtotime().

Creating a Cookie object as documented in a codebase that uses strict types will cause a TypeError.

In this PR, I'm widening the parameter type to string|int|null. This should not be a problem because while validating the value, we convert it back to a string anyway.