Problem

The license filter parameter accepts a comma-separated list of licenses.
The license_type filter parameter accepts comma-separated list of items like all, all-cc, commercial, and modification. These values are then converted into a list of the licenses that correspond to this category. For instance, license_type=commercial,modification URL search filter will be converted to ['by', 'sampling+', 'by-sa', 'cc0', 'pdm'] (excluding all of the ND and NC licenses).

Both of these filters are then converted to 2 separate ES terms queries: one with the list from license parameter, and another with the list of license_type values.

What should happen in an edge case when the user specifies a license that is outside of the specified license type? For instance, license=by-nd&license_type=commercial,modification that will create the following query:

"filter": [
        {
          "terms": {
            "license": ["by-nd"]
          }
        },
        {
          "terms": {
            "license": ["by", "sampling+", "by-sa", "cc0", "pdm"]
          }
        }
      ]

This query (https://api.openverse.engineering/v1/images/?format=json&license=by-nd&license_type=commercial,modification&page_size=1) will not return any results because the license queries are mutually exclusive.

@WordPress/openverse-maintainers, should we return an error response with a message that the license and license_type parameters are incompatible? Or should we just add a note to the API documentation, and keep returning an empty result as we do now?