merge option fails with multiple

[chrisroederucdenver]

Describe the bug
If you run with no arguments (as you very likely would not) you get: "ValueError: 'default' must be a list when 'multiple' is true."

To Reproduce
Steps to reproduce the behavior:

1. Go to the main directory
2. type ./main.py at the command line
3. See error as above

Expected behavior
I'd expect an error relating to the lack of arguments.

Screenshots
n/a

Desktop (please complete the following information):

• OS: macos Monterey
• bash

[callahantiff]

@chrisroederucdenver -- thanks so much for noting this and creating the PR to resolve it. I am currently deep in the next release and will definitely take a close look at this and if everything looks good, will include it with that release!