This can be used to check if a file set item has been assigned an output
format (e.g. fst, feather, qs or rds). If the check returns
FALSE it would signal that data should be returned rather than calling
write_stream().
This can be used to check if a file set item has been assigned an output
format (e.g. fst, feather, qs or rds). If the check returns
FALSE it would signal that data should be returned rather than calling
write_stream().