--- a/src/main/java/christie/codegear/CodeGear.java	Sat Dec 30 18:30:04 2017 +0900
+++ b/src/main/java/christie/codegear/CodeGear.java	Sat Dec 30 20:11:36 2017 +0900
@@ -47,6 +47,7 @@
     }
 
     public void checkAndSetCommand(Field field, String name){
+
         if (!field.getName().equals(name)){
             throw new IllegalArgumentException("key and DataGearName do not match");
         }
@@ -58,6 +59,10 @@
             e.printStackTrace();
         }
 
+        if (dg.getClazz() == null){
+            throw new NullPointerException("please initialize DataGear");
+        }
+
         commandList.add(new Command(this, dg, "local", name, CommandType.TAKE));
     }
 }