ST_AsGeoJSON can produce invalid geometry collections

[jyutzler]

After a slew of geometric operations, I ended up with an empty geometry collection. This was output as

"geometry":{  
            "type":"GeometryCollection",
            "geometries":null
         }

which is invalid. The "geometries" member must be the empty array [], not null.

​https://tools.ietf.org/html/rfc7946#section-3.1.8

If you need I can try to reproduce this, but the scenario was complicated and it might not be easy to do.

[dbaston]

Describing the slew of operations might be helpful.

[robe]

well our processing of empty geometry collections seems okay:

SELECT ST_AsGeoJSON('GEOMETRYCOLLECTION EMPTY'::geometry);

-- yields--
{"type":"GeometryCollection","geometries":[]}

And ingesting the above with null is invalid:

SELECT ST_GeomFromGeoJSON('{"type":"GeometryCollection", "geometries":null}');

-- yields

ERROR:  Unable to find 'geometries' in GeoJSON string

Is the "geometry: part something you are getting back? If getting back I'm assuming that is being tacked on by some post processor you have going and not part of what PostGIS is doing. If so your post processor might also be converting [] to nulls.

[pramsey]

Since we cannot reproduce I'm going to close out. Post the hexwkb of the offending feature if you happen to be able to re-generate it.