Power Query Custom Column: If date is null, calculate from another date column

I am attempting to write a formula in Power Query to add a new date column. The formula should add 90 days to a date in date column 1. if cell is null in date column 1 add 90 days to the date in date column 2. I have pasted me code below

= Table.AddColumn(#"Changed Type3", "90 Days", each if [#"Change Date (FT)"] = null then Date.AddDays([#"FT-Date"], 90) else Date.AddDays([#"Change Date (FT)"], 90)


I am receiving a syntax error: "Token RightParen expected."
Apologies if this has already been answered.

Thank you in advance.