wdfn-763 - Flip the default parameter code

Before making a pull request

• Put the appropriate EXEMPT flag if needed in the MR title (see https://practices.wma.chs.usgs.gov/practice/peer_code_review/)
• Run all linters (make lint)
• Run all tests (make test)
• Update the changelog appropriately
• If making a release, update code.json, versionNumber and metadataLastUpdated.

Description

The parameter code list is displayed in the opposite order of the period of record, so I changed the default parameter function to return the last list element.

After making a pull request

• If appropriate, put the link to the PR in the JIRA ticket
• Assign someone to review unless the change is trivial