Change data type in Custom function

let
Source = (Datefrom as nullable date, Dateto as nullable date) =>
let
ConvertedDatefrom = try Date.From(Datefrom) otherwise null,
ConvertedDateto = try Date.From(Dateto) otherwise null,
ResolvedDatefrom = if ConvertedDatefrom is null then ConvertedDateto else ConvertedDatefrom,
ResolvedDateto = if ConvertedDateto is null then ConvertedDatefrom else ConvertedDateto,
Dates = if ResolvedDatefrom <= ResolvedDateto
then List.Dates(ResolvedDatefrom, Duration.Days(Duration.From(ResolvedDateto - ResolvedDatefrom)) + 1, #duration(1, 0, 0, 0))
else List.Dates(ResolvedDateto, Duration.Days(Duration.From(ResolvedDatefrom - ResolvedDateto)) + 1, #duration(1, 0, 0, 0)),
Output = Table.FromList(Dates, Splitter.SplitByNothing(), {"Date.Date"})
in
Output
in
Source