Added 2 failing feature tests around empty GeoJSON data structures

[four43]

These two added tests fail with the latest tag 4.2.1 of node-mapnik. From what I understand these are valid GeoJSON (as checked against https://geojson.io)

[flippmoke]

@artemp is this an issue in our parser in mapnik core?

[artemp]

@four43 @flippmoke - {} is a valid JSON but is it a valid GeoJSON object?

https://tools.ietf.org/html/rfc7946

2.  GeoJSON Text

   A GeoJSON text is a JSON text and consists of a single GeoJSON
   object.

3.  GeoJSON Object

   A GeoJSON object represents a Geometry, Feature, or collection of
   Features.

   *  A GeoJSON object is a JSON object.

   *  A GeoJSON object has a member with the name "type".  The value of
      the member MUST be one of the GeoJSON types.

   *  A GeoJSON object MAY have a "bbox" member, the value of which MUST
      be a bounding box array (see Section 5).

   *  A GeoJSON object MAY have other members (see Section 6).
   

My reading (!) of the spec implies that while bbox and other members are optional, type is required. I think language is bit unfortunate here and I believe it has some historical background doh.

[four43]

@artemp thanks for weighing in on this. That's a good point and good referring to the spec. What do you think about the second test case in my pull request about the empty feature collection?

Thanks

[artemp]

@four43 - I think an empty collection is a valid GeoJSON and parser shouldn't fail but rather return an empty featureset

[artemp]

@four43 I created an issue mapnik/mapnik#4035 thanks for reporting!

[springmeyer]

tracking at mapnik/mapnik#4035