do not tile empty geojson, close #40

src/index.js

@@ -36,10 +36,10 @@ function GeoJSONVT(data, options) {
     features = wrap(features, options.buffer / options.extent, intersectX);
 
     // start slicing from the top tile down
-    this.splitTile(features, 0, 0, 0);
+    if (features.length) this.splitTile(features, 0, 0, 0);
 
     if (debug) {
-        console.log('features: %d, points: %d', this.tiles[0].numFeatures, this.tiles[0].numPoints);
+        if (features.length) console.log('features: %d, points: %d', this.tiles[0].numFeatures, this.tiles[0].numPoints);
         console.timeEnd('generate tiles');
         console.log('tiles generated:', this.total, JSON.stringify(this.stats));
     }

test/fixtures/empty.json

+{
+	"type": "FeatureCollection",
+	"features": []
+}

test/test-full.js

@@ -24,6 +24,11 @@ function testTiles(inputFile, expectedFile, maxZoom, maxPoints) {
     });
 }
 
+test('empty geojson', function (t) {
+    t.same(genTiles(getJSON('empty.json')), {});
+    t.end();
+});
+
 function getJSON(name) {
     return JSON.parse(fs.readFileSync(path.join(__dirname, '/fixtures/' + name)));
 }