Fixing the serializing issue of device groups.

components/policy-mgt/org.wso2.carbon.policy.mgt.common/src/main/java/org/wso2/carbon/policy/mgt/common/DeviceGroupWrapper.java

@@ -22,8 +22,12 @@ package org.wso2.carbon.policy.mgt.common;
 import io.swagger.annotations.ApiModel;
 import io.swagger.annotations.ApiModelProperty;
 
+import java.io.Serializable;
+
 @ApiModel(value = "DeviceGroupWrapper", description = "This class carries information related to device groups expect users and devices.")
-public class DeviceGroupWrapper {
+public class DeviceGroupWrapper implements Serializable {
+
+    private static final long serialVersionUID = 1998101722L;
 
     @ApiModelProperty(name = "id", value = "Id of the group", required = true)
     private int id;