We cannot apply field access to the type Null

I need to set a date for some type of data.

Namely when [Nature]="Information", the "End Date" is null and I need to replace that null value by whatever date is in the “Start Date” column.

#"Filtered Rows" = Table.SelectRows(#"Added Delay", each [Nature] <> null and [Nature] <> ""),
#"Fixed empty date" = Table.TransformColumns(#"Filtered Rows",{"End Date", each if [Nature]="Information" then [Start Date] else [End Date] })

Unfortunately I’m getting the following error, even though I made sure Nature is never null nor empty

Expression.Error: We cannot apply field access to the type Null.

Details:

    Value=

    Key=Nature

Any idea what’s going on?

Thanks