Azure Data Factory 2, Data flow with derived column, how to set a timestamp to null

Question

I have a Azure DataFactory V2 pipeline that executes a data flow.

The Azure Sql source table have a Date not null column, DateReported. This is imported from an external source. Where null values are 1899-01-01.

The destination Sql table have the same field, DateReported but as Date null

I'm using a Derived Column in my dataflow to sanitize data. I want to insert null when the date is 1899-01-01

My derived column function is this

iif(!(year(DateReported) == 1899 || year(DateReported) == 1753)
    , DateReported
    , null()
    )

This give me the error "Expression should return the same type 'timestamp' as previous expressions".

If I invert the iif to this

iif((year(DateReported) == 1899 || year(DateReported) == 1753)
    , null()
    , DateReported
    )

I get the error "Expression should return the same type 'null' as previous expressions"

I can fix this in sql from the source like this

Select ...
DateReported2 =
CASE
    WHEN DateReported is null THEN DateReported
    WHEN YEAR(DateReported) = 1899 THEN NULL
    ELSE DateReported
End
...

But this is messy, as all my other logic are in the dataflow.

How can I create a derived column that is a nullable timestamp, like C# DateTime? or SSIS NULL(DT_DATE)?

Solution:

case(year(DateReported) != 1899, DateReported)