Hi @SRJDB ,

Here is a work around, you can switch to the widget to text parameter and implement a enums. It helps in validation in both value as well as case check. Using enums in one of the best practices to use constant variables. More over you can add functions that can terminate the notebook gracefully if you have mentioned wrong values. 

You can use the below command to terminate the notebook,

dbutils.notebook.exit("Optional exit value or message")