Distinguish error message for empty list vs None.

[delucchi-cmu]

Change Description

Closes #341.

It's pretty common for users to use the result of a glob operation as input in the input_file_list argument. If the glob expression is mal-formed and the results are empty, they'll get a confusing error. This distinguishes the behavior from not passing in anything to hopefully give a more helpful message.

Code Quality

• [x] I have read the Contribution Guide and LINCC Frameworks Code of Conduct
• [x] My code follows the code style of this project
• [x] My code builds (or compiles) cleanly without any errors or warnings
• [x] My code contains relevant comments and necessary documentation

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.72%. Comparing base (28af48b) to head (46e1221).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #367 +/- ## ======================================= Coverage 99.72% 99.72% ======================================= Files 26 26 Lines 1457 1460 +3 ======================================= + Hits 1453 1456 +3 Misses 4 4 ```

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