TypeScript errors in custom overlay example

[phibo23]

I am implementing a custom map control based on the "custom overlay" example: https://github.com/visgl/react-map-gl/blob/f903e44593e67a320fbe3257f0a2b687e7061cbd/examples/custom-overlay/src/custom-overlay.tsx

It works fine and I was able to adapt it to my requirements, but when I build my code (as part of a Next.js project) I am getting some TypeScript errors such as:

I am not familiar enough with the types used by the library internally to find a proper solution. Currently I just added @ts-ignore to all affected lines.

[Pessimistress]

If your tsconfig has strictNullCheck then just type _map as MapInstance | null.