[9.x] Null value for auto-cast field caused deprication warning in php 8.1

[JBtje]

Problem:

• PHP 8.1 no longer supports null for json_decode, and throws a deprication warning
  https://wiki.php.net/rfc/deprecate_null_to_scalar_internal_arg
  Changed in php/php-src@b10416a#diff-a39ce231303cec12a6d347165931a7f2209ee7dce5989f2e06f8c04143ec7032

However, thr RFC says that null is a valid JSON value:
https://datatracker.ietf.org/doc/rfc8259/

A JSON value MUST be an object, array, number, or string, or one of
the following three literal names:

    false null true

 The literal names MUST be lowercase.  No other literal names are
 allowed.

Thus, auto cast should accept null as a valid JSON and not result in a deprecation warning..

also see issue #43705

[driesvints]

Please provide a thorough explanation and don't just link to an issue. Otherwise this will get closed.

[marcovo]

The reasoning based on the RFC is not entirely solid. It is true that false, true and null are valid JSON literals, but translating to php, this would mean that the following three statements should successfully return the respective values (which they do):

json_decode('true')
json_decode('false')
json_decode('null')

Here, 'null' is the null described by the RFC. This is something else than:

json_decode(null)

i.e., the null literal instead of the string 'null'.

While the submitted change is probably perfectly valid, this would be primarily to conform to php's new function signature. The RFC argument is not valid here.
Also, missing a test here?

[driesvints]

@marcovo did this break something for you? If so how is that reproducable?

[marcovo]

It did not break anything for me; merely pointing out that in the opening post, the deprecation warning is a valid point but the RFC argument is not applicable. Ultimately the change seems fine.

[driesvints]

@marcovo right, gotcha.

[kayw-geek]

@driesvints #43507 So should it be shut down instantly?

[driesvints]

@kayw-geek you didn't exactly explain where this issue was coming from as well as the people in #43705 did. Afaik you could be calling the method directly. Next time please provide a more thorough explanation and your PR might have been accepted.

[kayw-geek]

@kayw-geek you didn't exactly explain where this issue was coming from as well as the people in #43705 did. Afaik you could be calling the method directly. Next time please provide a more thorough explanation and your PR might have been accepted.

OK, I'll write it in detail later.