A GeoJSON object with type "GeometryCollection" is a Geometry object.
A GeometryCollection has a member with the name "geometries".
The value of "geometries" is an array. Each element of this array is a GeoJSON Geometry object.
It is possible for this array to be empty.
GeometryCollection
https://tools.ietf.org/html/rfc7946#section-3.1.8
A GeoJSON object with type "GeometryCollection" is a Geometry object. A GeometryCollection has a member with the name "geometries". The value of "geometries" is an array. Each element of this array is a GeoJSON Geometry object. It is possible for this array to be empty.