Bug report

Under certain circumstances (see example), the array union operator ('+'), will always assume its output to be non-empty, even if this is not necessarily the case.

array_merge does not have this problem, but since its behaviour is different, it's not a drop-in replacement

Code snippet that reproduces the problem

https://phpstan.org/r/016cc695-a104-4dac-8ad5-10bbc1c6d01d

Expected output

array<string, string>

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