Fix null pointer exception in with-react-18next (#3944)
Fix null pointer exception in with-react-18next (#3944)

The example does not crash if a user chooses a non-existing language (e.g. goes to localhost:3000/?lng=ru)
zeit/next.js,flybayer/next.js,flybayer/next.js,flybayer/next.js,azukaru/next.js,JeromeFitz/next.js,JeromeFitz/next.js,zeit/next.js,zeit/next.js,azukaru/next.js,azukaru/next.js,BlancheXu/test,BlancheXu/test,JeromeFitz/next.js,flybayer/next.js,BlancheXu/test,azukaru/next.js,JeromeFitz/next.js