You should be catching NullPointerException with the code above, but that doesn't change the fact that your Check_Circular is wrong. If you fix Check_Circular, your code won't throw NullPointerException in the first place, and work as intended.
Try:
public static boolean Check_Circular(LinkedListNode head)
{
LinkedListNode curNode = head;
do
{
curNode = curNode.next;
if(curNode == head)
return true;
}
while(curNode != null);
return false;
}