Let users implement their own VectorTileEncoder.clipGeometry.

For use with GeoTools GeometryClipper or whatever.

src/main/java/no/ecc/vectortile/VectorTileEncoder.java

@@ -58,11 +58,11 @@ public class VectorTileEncoder {
 
     private final double minimumArea;
 
-    private final Geometry clipGeometry;
+    protected final Geometry clipGeometry;
 
-    private final Envelope clipEnvelope;
+    protected final Envelope clipEnvelope;
 
-    private final PreparedGeometry clipGeometryPrepared;
+    protected final PreparedGeometry clipGeometryPrepared;
 
     private final boolean autoScale;
 
@@ -223,7 +223,7 @@ public void addFeature(String layerName, Map<String, ?> attributes, Geometry geo
         }
 
         // no need to add empty geometry
-        if (geometry.isEmpty()) {
+        if (geometry == null || geometry.isEmpty()) {
             return;
         }