I guss this.location
or this.location.selecteditem
may be null, So you got that error.
So please try this if
condition instead of your if
condition way
if(this.location != null && this.location.selecteditem !=null && this.location.selecteditem.locationID != null)
{
//Write your code here
}
So your final code look like
if(this.location == null && this.location.selecteditem ==null && this.location.selecteditem.locationID == null)
{
this.ShowMessageBox("test"); //not sure what to put there so I just made something up
}
else if (this.location.SelectedItem.locationID.Contains("CMP"))
{
this.FindControl("datePurchased").IsVisible = true;
this.FindControl("age").IsVisible = true;
this.FindControl("userList").IsVisible = true;
}
else
{
this.FindControl("datePurchased").IsVisible = false;
this.FindControl("age").IsVisible = false;
this.FindControl("userList").IsVisible = false;
}