Selecting only one f:checkbox in Spring gives error

I have an implementation where when user click on checkbox , a json gets associated as value of checkbox and that value is passed to my bean class. And In the method invoked, the String is then parsed into JSON object. When I select two checkbox, it works perfectly fine. But if I select one checkbox, then it gives me error.

Here is my Checkbox Bean class -

private ArrayList<String> Ancillary=new ArrayList<String>()  ;


public ArrayList<String> getAncillary() {
    for(int i=0;i<Ancillary.size();i++){
    System.out.println(i+"Object:" +Ancillary.get(i)+"\n\n\n");
    }
    return Ancillary;
}

public void setAncillary(ArrayList<String> ancillary) {
    Ancillary = ancillary;
}

Here is my method where I print value of a Particular key in JSON.

public Event updatePax(RequestContext context) throws Exception {
    ExtrasMenu extrasMenu = (ExtrasMenu) context.getConversationScope().get(ScopeKeys.EXTRASMENU);
    System.out.println("As a string:"+extrasMenu.getAncillary().toString());
    JSONObject json=new JSONObject(extrasMenu.getAncillary().get(0));
    System.out.println(json.get("firstName"));
   }

And here is the Output-

If only one checkbox is selected -

0Object:{"firstName":"TIMOTHY"
1Object:"lastName":"WALKER"
2Object:"price":100
3Object:"meals":["Vegeterian Food"]}

If two or more checkboxes are selected -

0Object:{"firstName":"TIMOTHY","lastname":"WALKER","price":"50","Ordinal":"PET_SERVICES"}
1Object:{"firstName":"ANNE","lastname":"WALKER","price":"150","Ordinal":"PARKING_SERVICE"}