Sorry. I still don’t understand your question.
If data is missing, what is the problem ? I have nothing to deal with. If the data is invalid (NaN), I can remove it from my data set or skip it when processing the data.
In Go there is no “null” value for a float, but you could replace it with a NaN which is a special value.
If you need to marshall to JSON a floating point value that can be a NaN, I would suggest to define your own type and associated marshalling and unmarshal functions that will convert NaN <-> null.