nan is a ieee754-defined error. what javascript calls errors these days (it tends to change a lot) has little to nothing to do with that. it's on every developer to familiarise themself with ieee754, it's one of the most important documents in the profession.

while nan is an invalid floating-point number, it is a valid value for a float-typed field. making it into an error is like adding a bit labelled "crash" to every number in your program.