Fix USGS RDC missing value bug

[dschristianson]

Issue #158

Note: this fix does not address the full issue ticket. It only fixes the USGS bug rather than comprehensive basin3d missing value support.

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• [x] Unit tests
• [x] Integration tests
• [x] Test coverage >= 90%
• [x] Flake8 Tests
• [x] Mypy Tests
• [ ] Other -

Test Configuration

• Python Version: 3.9

PR Self Evaluation

strikethrough things that don’t make sense for your PR

• [x] My code follows the agreed upon best practices
• [x] I have commented my code, particularly in hard-to-understand areas ~- [ ] I have made corresponding changes to the documentation~
• [x] My changes generate no new warnings
• [x] I have added tests or modified existing tests that prove my fix is effective or that my feature works
• [x] Existing unit tests pass locally with my changes ~- [ ] Any dependent changes have been merged and published in the appropriate modules~
• [x] I have performed a self-review of my own code