GeometryCollection(g [, g] ...)

Constructs a GeometryCollection value from the geometry arguments.

GeometryCollection() returns all the proper geometries contained in the
arguments even if a nonsupported geometry is present.

GeometryCollection() with no arguments is permitted as a way to create
an empty geometry.

URL: https://dev.mysql.com/doc/refman/5.7/en/gis-mysql-specific-functions.html

