public Edge get(){
		if(lastStack == null || Configuration.hasEdgeTypeChanged()){
			lastStackTypeName = Configuration.getEdgeType();
			lastStack = stacks.get(lastStackTypeName);
			if(lastStack == null) {
				lastStack = new Stack<Edge>();
				stacks.put(Configuration.getEdgeType(), lastStack);
			}
		}
		if(lastStack.empty()){
			return null;
		}
		return lastStack.pop();
	}