Allow GeoJSON features with id equal to 0

fixes #4326

src/ol/format/geojsonformat.js

@@ -408,7 +408,7 @@ ol.format.GeoJSON.prototype.readFeatureFromObject = function(
     feature.setGeometryName(this.geometryName_);
   }
   feature.setGeometry(geometry);
-  if (geoJSONFeature.id) {
+  if (geoJSONFeature.id !== undefined) {
     feature.setId(geoJSONFeature.id);
   }
   if (geoJSONFeature.properties) {

test/spec/ol/format/geojsonformat.test.js

@@ -27,6 +27,15 @@ describe('ol.format.GeoJSON', function() {
     }
   };
 
+  var zeroIdGeoJSON = {
+    'type': 'Feature',
+    'id': 0,
+    'geometry': null,
+    'properties': {
+      'prop0': 'value0'
+    }
+  };
+
   var lineStringGeoJSON = {
     'type': 'Feature',
     'geometry': {
@@ -166,6 +175,12 @@ describe('ol.format.GeoJSON', function() {
       expect(feature.get('prop0')).to.be('value0');
     });
 
+    it('can read a feature with id equal to 0', function() {
+      var feature = format.readFeature(zeroIdGeoJSON);
+      expect(feature).to.be.an(ol.Feature);
+      expect(feature.getId()).to.be(0);
+    });
+
     it('can read a feature collection', function() {
       var features = format.readFeatures(featureCollectionGeoJSON);
       expect(features).to.have.length(3);