How to make/set "IM_Assert()"

[CodingMadness]

Title.

the ocornut guy from ImGui told me I need to set this so I can see further information when something crashes, by whoever fault it is.

I can't see that method anywhere in the current ImGui lib. Any help to this would be much appreciated :) And btw nicely done with this lib so we can utilize lovely imGui in C# swell :D