Type Error: current ZoneSite

[benwalch]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no

In different scenarios, the following Error occurred:

TypeError

I18nBundle\Context\I18nContext::getCurrentZoneSite(): Return value must be of type I18nBundle\Model\ZoneSiteInterface, null returned

The return type of determinateCurrentZoneSite() in https://github.com/dachcom-digital/pimcore-i18n/blob/master/src/Context/I18nContext.php#L277 is nullable, also the property currentZoneSite.
Therefore, cases may occur, where currentZoneSite of the i18n context is null.

But the return type of getCurrentZoneSite() in https://github.com/dachcom-digital/pimcore-i18n/blob/master/src/Context/I18nContext.php#L66 is non-nullable.
Calling this getter when the property is null leads to this error and the whole thing crashes

[tomhatzer]

We also have this problem now and don't know how to solve it or why it occurs only in special places. It does not happen on every page but only single ones that have been copied to different languages. Every other page works well without that exception. From what we can see in the Pimcore backend the settings are the same as for every other page inside a language.