Exception in thread "main" java.lang.NullPointerException
at dataming_ID3.ID3Tool.buildDecisionTree(ID3Tool.java:291)
at dataming_ID3.ID3Tool.buildDecisionTree(ID3Tool.java:319)
at dataming_ID3.ID3Tool.buildDecisionTree(ID3Tool.java:319)
at dataming_ID3.ID3Tool.startBuildingTree(ID3Tool.java:392)
at dataming_ID3.Client.main(Client.java:11)