Bug report

According to the docs, $a ?? $b is functionally equivalent to isset($a) ? $a : $b. However, PHPstan seems to treat them differently.

Code snippet that reproduces the problem

See lines 14 (null coalescing) and 15 (isset) of the following:

https://phpstan.org/r/ff7c5d16-abb6-4445-b950-1799077559ce

An error is produced for line 14 (null coalescing):

Access to an undefined property object::$datalen

but not for line 15 (isset).

Expected output

No error should be produced for line 14.

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