Any plans to make `null_to_na()` an exported function?

[ramiromagno]

I find null_to_na() a rather useful function:

https://github.com/jeroen/jsonlite/blob/a68e1d46e2ae6450cd46c12be0e32fd66d12a90c/R/null_to_na.R#L1-L4

I would like to use null_to_na in a package but calling it as jsonlite:::null_to_na() raises a note with devtools::check():

checking dependencies in R code ... NOTE
Unexported object imported by a ':::' call: ‘jsonlite:::null_to_na’

[jefferis]

@alexanderbates FYI

[chrisknoll]

I'm running into same issue: we're using the jsonlite function null_to_na to convert nulls to NA in object...but this isn't an exported function.

Is it that difficult to add @export to this function?