Check an indicator filter before the catalogue is fetched: an object with no key but
theme, year and search (assertKnownKeys), a theme or search
that is set must not be blank ("" or whitespace), because a blank filter would
match every indicator, and a year must be a 4-digit year (normaliseYearFilter).
Throws RegionalatlasValidationError (Invalid search: Expected a non-empty value.).
Check an indicator filter before the catalogue is fetched: an object with no key but
theme,yearandsearch(assertKnownKeys), athemeorsearchthat is set must not be blank ("" or whitespace), because a blank filter would match every indicator, and ayearmust be a 4-digit year (normaliseYearFilter). ThrowsRegionalatlasValidationError(Invalid search: Expected a non-empty value.).