Difficult for me to debug!
Could you try adding the $serial_port variable to the error message to see what is actually set?
I’d quite like to be able to get to the root of the issue.
The $serial_port variable translates to null in the error message
@TrystanLea or @emrys - can you chip in please. If it is null I’d have expected the isset to return false and not hit this code.
@Berten_Du_Bruyn - I’ve got to the limit of my PHP I’m afraid!