can't facet on gmp_library_path

[willkg]

I tried to facet on gmp_library_path with supersearch facet. It's a protected field, so it requires a token with view pii access. When I try to facet on this field, I get this:

$ supersearchfacet --_facets=gmp_library_path --dotenv --verbose --_return_query=1
Using API token: SOMETOKEN
Params: {'_facets': ['gmp_library_path'], '_return_query': ['1'], 'date': ['>=2025-01-28 00:00:00', '<2025-02-04 23:59:59']}
supersearch_facet: url: https://crash-stats.mozilla.org/api/SuperSearch/, params: {'_facets': ['gmp_library_path'], '_return_query': ['1'], 'date': ['>=2025-01-28 00:00:00', '<2025-02-04 23:59:59'], '_results_number': 0}
DEBUG:urllib3.connectionpool:Starting new HTTPS connection (1): crash-stats.mozilla.org:443
DEBUG:urllib3.connectionpool:https://crash-stats.mozilla.org:443 "GET /api/SuperSearch/?_facets=gmp_library_path&_return_query=1&date=%3E%3D2025-01-28+00%3A00%3A00&date=%3C2025-02-04+23%3A59%3A59&_results_number=0 HTTP/11" 200 600
{
    'query': {
        'query': {
            'filtered': {
                'query': {'match_all': {}},
                'filter': {'bool': {'must': [{'bool': {'must': [{'range': {'processed_crash.date_processed': {'lt': '2025-02-04T23:59:59+00:00'}}}, {'range': {'processed_crash.date_processed': {'gte': '2025-01-28T00:00:00+00:00'}}}]}}]}}
            }
        },
        'aggs': {'signature': {'terms': {'field': 'processed_crash.signature.full', 'size': 50}}},
        'from': 0,
        'size': 0,
        'fields': ['processed_crash.uuid', 'processed_crash.date_processed', 'processed_crash.signature', 'processed_crash.product', 'processed_crash.version']
    },
    'indices': ['socorro202505', 'socorro202504']
}

It looks like Super Search API is dropping the gmp_library_path field from the facets.

When I facet on it with the webapp interface, it works fine:

https://crash-stats.mozilla.org/search/?gmp_library_path=%21__null__&product=Firefox&date=%3E%3D2025-01-29T01%3A49%3A00.000Z&date=%3C2025-02-05T01%3A49%3A00.000Z&_facets=signature&_facets=gmp_library_path&_sort=-date&_columns=date&_columns=signature&_columns=product&_columns=version&_columns=build_id&_columns=platform&_columns=gmp_library_path#crash-reports

Why?