Basically as I said above, “if a 3rd-party library calls C (or other) function or external program” - so you have a C library Foo, a Julia wrapper Foo.jl which just ccall’s the C code and performs some postprocessing calculations. If you as the package user want to evaluate function from Foo.jl in a region they are not defined, all you get is an exception instead of e.g. an array where only the out-of-bounds values are NaN’s.
This is an actual case I have in Python now, and there it obviously works fine - all NaNs propagate straight to the final result. Was looking for simplest ways to port and the library to julia.