FeatureGraphGenerator decorates PolygonGraphGenerator.
In case of adding node, FeatureGraphGenerator makes Graphable object with Polygon geometry by decorate generator.
After making Graphable object, FeatureGraphGenerator changes it's object to feature(SimpleFeature).
Method in FeatureGraphGenerator
When finding Node in PolygonGraphGenerator, it assume that found node has Polygon object.
but actually, Node has SimpleFeatureImpl, so it throws ClassCastExcpetion.
Method in PolygonGraphGenerator