default values for `mutlivalued=True` params now must be lists

[keighrim]

additional fix for #197

[codecov[bot]]

Codecov Report

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

Project coverage is 74.49%. Comparing base (ef4b59c) to head (906c486). Report is 5 commits behind head on develop.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #203 +/- ## =========================================== + Coverage 74.39% 74.49% +0.10% =========================================== Files 9 9 Lines 738 745 +7 =========================================== + Hits 549 555 +6 - Misses 189 190 +1 ``` | [Flag](https://app.codecov.io/gh/clamsproject/clams-python/pull/203/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=clamsproject) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/clamsproject/clams-python/pull/203/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=clamsproject) | `74.49% <100.00%> (+0.10%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=clamsproject#carryforward-flags-in-the-pull-request-comment) to find out more.

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