Confusing Question on Missouri Form MO-1040 Line 44 (Amendment)

[JR108]

Using TurboTax Deluxe on my PC, I amended my Arizona 2021 return to claim credit for taxes already paid in Missouri. I made no changes to my Federal or Missouri returns. TurboTax brings up the MO-1040 form and asks me to fill the filing "date of my Federal amended return if filed." 

Since I did not file or need to file an amended Federal return, I tried leaving that unfilled, but TurboTax keeps flagging that as an item that needs review. 

How should I handle this - leave the date unfilled, or fill the date of my original Federal return, or amend the Federal return (which requires no change)? 

Thanks.