Support null feature geometries

lib/geo/json/decoder.ex

@@ -30,8 +30,11 @@ defmodule Geo.JSON.Decoder do
 
   @doc """
   Takes a map representing GeoJSON and returns a Geometry.
+
+  Feature objects with null geometries will be stripped from a FeatureCollection,
+  and a standalone Feature object with null geometry will be decoded to nil.
   """
-  @spec decode!(map()) :: Geo.geometry()
+  @spec decode!(map()) :: Geo.geometry() | nil
   def decode!(geo_json) do
     cond do
       Map.has_key?(geo_json, "geometries") ->
@@ -72,14 +75,16 @@ defmodule Geo.JSON.Decoder do
 
       Map.get(geo_json, "type") == "FeatureCollection" ->
         geometries =
-          Enum.map(Map.get(geo_json, "features"), fn x ->
+          Map.get(geo_json, "features")
+          |> Enum.map(fn x ->
             do_decode(
               Map.get(x, "type"),
               Map.get(x, "geometry"),
               Map.get(x, "properties", %{}),
               Map.get(x, "id", "")
             )
           end)
+          |> Enum.reject(&is_nil/1)
 
         %GeometryCollection{
           geometries: geometries,
@@ -94,7 +99,7 @@ defmodule Geo.JSON.Decoder do
   @doc """
   Takes a map representing GeoJSON and returns a Geometry.
   """
-  @spec decode(map()) :: {:ok, Geo.geometry()} | {:error, DecodeError.t()}
+  @spec decode(map()) :: {:ok, Geo.geometry() | nil} | {:error, DecodeError.t()}
   def decode(geo_json) do
     {:ok, decode!(geo_json)}
   rescue
@@ -168,6 +173,8 @@ defmodule Geo.JSON.Decoder do
     %MultiPolygonZ{coordinates: coordinates, srid: get_srid(crs), properties: properties}
   end
 
+  defp do_decode("Feature", nil, _properties, _id), do: nil
+
   defp do_decode("Feature", geometry, properties, _id) do
     do_decode(Map.get(geometry, "type"), Map.get(geometry, "coordinates"), properties, nil)
   end

test/geo/json_test.exs

@@ -301,6 +301,43 @@ defmodule Geo.JSON.Test do
     assert geom1.properties["label"] == "8 Boulevard du Port 80000 Amiens"
   end
 
+  test "Decode feature with null geometry" do
+    json = """
+      {
+        "properties": {
+          "context": "80, Somme, Picardie",
+          "housenumber": "8"
+        },
+        "geometry": null,
+        "type": "Feature"
+      }
+    """
+
+    geom = Jason.decode!(json) |> Geo.JSON.decode!()
+    assert is_nil(geom)
+  end
+
+  test "Decode feature in a feature collection with null geometry" do
+    json = """
+      {
+        "type": "FeatureCollection",
+        "features": [
+          {
+            "properties": {
+              "context": "80, Somme, Picardie",
+              "housenumber": "8"
+            },
+            "geometry": null,
+            "type": "Feature"
+          }
+        ]
+      }
+    """
+
+    geom = Jason.decode!(json) |> Geo.JSON.decode!()
+    assert geom.geometries == []
+  end
+
   property "encodes and decodes back to the correct Point struct" do
     check all x <- float(),
               y <- float() do