How to tell dockspace to fill entire available space when trying to dock first window?

[BreyerW]

NoSplit dock flag is extremely close, the problem is, it persist after first window was docked which is NOT what i want. And ideally i would like to still have 5 docking spots instead of only central being rendered. The idea is that i dont want accidental empty spaces between docked windows. Just checking on empty dockspace would solve most cases i think

And i dont want to rely on imgui_internal since i rely on ImGUI.NET which is c# binding and this in turn rely on cimgui and since imgui_internal is still considered, well, internal, not many binding authors bothered to bind against that.