Unexpected Operand Exception

package exercises;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;
import java.util.Random;
/**
 * For this program, you must give a list of 4 items, the 3 objects to me moved across the River,
 * and "You". Object 1 cannot be together with object 2, and object 2 cannot be together
 * with object 3.
 * @author theif519
 */
public class RiverCrossing {
    private class River
    {
        Collection<String> order = new ArrayList<String>();
        List<String> listOfCharacters = null;
        Collection<String> otherSide = null;
        public River(List<String> listOfCharacters)
        {
            this.listOfCharacters = listOfCharacters;
            this.otherSide = listOfCharacters;
        }

        public boolean attemptTransport(String object, Option option)
        {
            if(option.equals(option.ADD))
            {
                return addAttempt(object);
            }
            else if(option.equals(option.REMOVE))
            {
                return removeAttempt(object);
            }
            else
            {
                return false;
            }

        }
        public boolean removeAttempt(String object)
        {
            otherSide.add(object);
            otherSide.add("You");
            order.remove(object);
            order.remove("You");
            if(otherSide.containsAll(Arrays.asList(listOfCharacters.get(0),listOfCharacters.get(1))))
            {
                otherSide.remove(object);
                otherSide.remove("You");
                order.add(object);
                order.add("You");
                return false;
            }
            else if(otherSide.containsAll(Arrays.asList(listOfCharacters.get(1),listOfCharacters.get(2))))
            {
                otherSide.remove(object);
                otherSide.remove("You");
                order.add(object);
                order.add("You");
                return false;
            }
            else
            {
                return true;
            }
        }
        public boolean addAttempt(String object)
        {
            otherSide.remove(object);
            otherSide.remove("You");
            order.add(object);
            order.add("You");
            if(otherSide.containsAll(Arrays.asList(listOfCharacters.get(0),listOfCharacters.get(1))) && !otherSide.contains("You"))
            {
                otherSide.add(object);
                otherSide.add("You");
                order.remove(object);
                order.remove("You");
                return false;
            }
            else if(otherSide.containsAll(Arrays.asList(listOfCharacters.get(1),listOfCharacters.get(2))) && !otherSide.contains("You"))
            {
                otherSide.add(object);
                otherSide.add("You");
                order.remove(object);
                order.remove("You");
                return false;
            }
            else
            {
                return true;
            }
        }
    }
    public enum Option
    {
        ADD, REMOVE;
    }
    public static void main(String[] args)
    {
        RiverCrossing test = new RiverCrossing();
        test.computeSolution();
    }
    public void computeSolution()
    {
        List<String> list = Arrays.asList("Wolf", "Goat", "Salad", "You");
        Random random = new Random();
        River river = new River(list);
        while(!river.order.containsAll(list))
        {
            if(river.addAttempt(list.get(random.nextInt(2))) == false)
            {
                continue;
            }
            else
            {
                System.out.println(river.otherSide + "\n" + river.order);
            }
            if(river.removeAttempt(list.get(random.nextInt(2))) == false)
            {
                while(true)
                {
                    if(river.removeAttempt(list.get(random.nextInt(2))) == true)
                    {
                        break;
                    }
                }
            }
            else
            {
                System.out.println(river.otherSide + "\n" + river.order);
            }
        }
    }
}