new poster and new to stack exchange. I apologise if this has been answered but i am unable to find a solution sifting through the posts here.
I am getting a null reference exception on a very basic health bar script.
HealthBar script:
using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class HealthBars : MonoBehaviour {
    public GameObject pug;
    private Animator animator;
    public Slider healthBar;
    public Slider waterBar;
    public Slider poopBar;
    public Slider weeBar;
    public Slider foodBar;
    public static int health = 100;
    public static int wee = 0;
    public static int food = 25;
    public static int poop = 0;
    public static int water = 50;
    // Use this for initialization
    void Start()
    {
        InvokeRepeating("ReduceFood", 1, 1);
        InvokeRepeating("WaterDrain", 1, 1);
    }
    // Update is called once per frame
    void Update ()
    {
    }
    void ReduceFood()
    {
        food = food - 5;
        foodBar.value = food;
    }
    void WaterDrain()
    {
        water = water - 2;
        waterBar.value = water;
    } 
I have the script attached to an empty GameObject. It drains the food once then throws the exception?
 
    