release_date issue

Hi,

I have a serie of queries like

https://www.giantbomb.com/api/releases/?api_key=mdsdkln8d9y98cdys8dssd9dsuuib5f24ac4e2dcf0e&format=json&field_list=name,release_date,expected_release_day,expected_release_month,platform&filter=release_date:2018-10-16

resulting in response containing usually expected_release_day,expected_release_month and null release_date. See below:

{"error":"OK","limit":100,"offset":0,"number_of_page_results":6,"number_of_total_results":"6","status_code":1,"results":[{"expected_release_day":16,"expected_release_month":10,"name":"The Packet Queen #","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-94\/","id":94,"name":"PC"},"release_date":null},{"expected_release_day":16,"expected_release_month":10,"name":"Starlink: Battle for Atlas","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-157\/","id":157,"name":"Nintendo Switch"},"release_date":null},{"expected_release_day":16,"expected_release_month":10,"name":"Crayola Scoot","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-157\/","id":157,"name":"Nintendo Switch"},"release_date":null},{"expected_release_day":16,"expected_release_month":10,"name":"Big Buck Hunter Arcade","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-157\/","id":157,"name":"Nintendo Switch"},"release_date":null},{"expected_release_day":16,"expected_release_month":10,"name":"LEGO DC Super-Villains","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-157\/","id":157,"name":"Nintendo Switch"},"release_date":null},{"expected_release_day":16,"expected_release_month":10,"name":"Warriors Orochi 4","platform":{"api_detail_url":"https:\/\/www.giantbomb.com\/api\/platform\/3045-157\/","id":157,"name":"Nintendo Switch"},"release_date":null}],"version":"1.0"}

Why the release_date works in filter but do not return result as a field?