error this code

void android.widget.LinearLayout.setBackgroundColor(int)' on a null object reference

in ShowDayViewEventsListAdapter class
and this line 

`
 if (!AppConstants.strEventCellBackgroundColor.equals("null")) {
                        ll_month_events.setBackgroundColor(Color.parseColor(AppConstants.strEventCellBackgroundColor));
                    }
`

please help