DataObject#clone() 추가

src/main/java/cokr/xit/foundation/data/DataObject.java

@@ -124,4 +124,10 @@ public class DataObject extends StringMap<Object> {
 		Boolean bool = obj instanceof Boolean b ? b : Boolean.valueOf(obj.toString());
 		return bool.booleanValue();
 	}
+
+	@Override
+	public DataObject clone() {
+		Object copy = super.clone();
+		return (DataObject)copy;
+	}
 }