applescript Add time to selected photos on photos.app

Hi i tried to create a script to add some minutes to selected photos in photos.app

But i have a random error on handler.

This is my script:

display dialog "Give me number of minutes to increment" default answer ""

set timeIncrement to text returned of result as integer

tell application "Photos"

activate

set imageSel to (get selection)

set counter to 0

if imageSel is {} then

error "Please select some images."

else

repeat with im in imageSel

tell im

set tmp_date to its date

set new_date to tmp_date + (timeIncrement * minutes)

set counter to counter + 1

set its date to new_date

delay 0.1

end tell

end repeat

end if

return "Adjusted the date and time of " & counter & " photos."

end tell

What is the problem?