False positive: null check condition in nested method

[JanMikes]

Summary of a problem or a feature request

It would be awesome, if there is nullability check in other method, to recognise that variable can not be null anymore.

Code snippet that reproduces the problem

https://phpstan.org/r/4e1685f6643e62a6eb8ed7c9fb31d482

	/** @var null|string */
	private $a;

	public function hasA(): bool
	{
		return $this->a !== null;	
	}
	
	
	public function getA(): string
	{
		if (false === $this->hasA()) {
			throw new \LogicException();
		}
		
		return $this->a;
	}

Expected output

I expected no errors as it seems to be valid PHP code to me.

[ondrejmirtes]

This has been discussed many times 😊

See #534, #634, #201.