Should X display/connection handles be nullable?

[madsmtm]

XlibDisplayHandle.display and XcbDisplayHandle.connection are nullable; should they be?

Previously discussed in #136.

[notgull]

If I remember correctly, display handles can be null for EGL. I've changed my mind since my posts in #136, I think allowing this use case is worth it.

[kchibisov]

Yes, there's a thing called EGL_DEFAULT_DISPLAY, so it'll use the display somehow automatically. Also it does open connection under the hood with xcb iirc the mesa code.

[i509VCB]

Whether null is correct depends on the context. Like kchibisov, for EGL it is valid. Meanwhile in Vulkan, you must provide a valid pointer to a display.