PR Summary

Simplified a bit of code related to masked arrays.

• basic_units: already converted to non-masked a few lines up
• ticker: may just as well use the MaskedConstant class (clearer, only a single check)
• MaskedArray is a subclass of nparray

(Was about to change many isinstance(.., MaskedArray) to is_masked, but the time for is_masked is much higher compared to isinstance(), so while it probably will be beneficial in the few cases where a MaskedArray object does not have any masked content, this seems a bit too exotic. One may consider the opposite though, replace is_masked with isinstance.)

PR Checklist

Documentation and Tests

• Has pytest style unit tests (and pytest passes)
• Documentation is sphinx and numpydoc compliant (the docs should build without error).
• New plotting related features are documented with examples.

Release Notes

• New features are marked with a .. versionadded:: directive in the docstring and documented in doc/users/next_whats_new/
• API changes are marked with a .. versionchanged:: directive in the docstring and documented in doc/api/next_api_changes/
• Release notes conform with instructions in next_whats_new/README.rst or next_api_changes/README.rst