From the documentation:
The values you give to these task-scoped variables will automatically populate the values for the script and there is no need for additional expressions in the tasks properties to be created to set the values.
Please be aware of the following note for non-required parameters in cases when you are not seeing their corresponding task-scoped variables:
Example: variable is not visible
Example: variable is visible
Once the parameter has been given a value, the task-scoped variable will persist whether a value is given or not in the editor.