My experience on this project was that the checks proved to be useful way before I could run the program for the first time.
The first version of the code had relatively few null checks. Later I went through and added them consistently at function boundaries, and that process ended up revealing a surprising number of bugs and bad assumptions.
Sanitizers and static analyzers could have surely caught many of these issues later, but adding the checks was a useful way to reason about the code while writing it. It felt less defensive and more proactively preventive.
