Why do I keep getting 'The object you want to instantiate is null' warning?

I'm a beginner in C# and I'm currently working on script for my 2D game, where I would like random objects to fall from the top of the screen, from random locations, however for some reason, when I run my game in Unity, I keep getting a warning that says:

'Arguement Exception: The Object you want to Instantiate is null. UnityEngine.Object.CheckNullArgument.'

Anyone know how to fix this ?

 public class FallingObjectBehaviour : MonoBehaviour {
 
     public float spawnTime =3f;
     public GameObject[] FallingObjects;
     public Transform[] spawnPoints;
     public int FallingObjectsSpawn;
     public float fallSpeed = 10f;
 
     void Start () {
         FallingObjects = new GameObject[5];
         FallingObjects [0] = GameObject.FindGameObjectWithTag ("Cherry");GetComponent<SpriteRenderer> ();
         FallingObjects [1] = GameObject.FindGameObjectWithTag ("Strawberry");GetComponent<SpriteRenderer> ();
         FallingObjects [2] = GameObject.FindGameObjectWithTag ("Apple");GetComponent<SpriteRenderer> ();
         FallingObjects [3] = GameObject.FindGameObjectWithTag ("Grape");GetComponent<SpriteRenderer> ();
         FallingObjects [4] = GameObject.FindGameObjectWithTag ("Bomb");GetComponent<SpriteRenderer> ();
 
     }
 
     void Update () {
         
         FallingObjectsSpawn = Random.Range (0, 4); 
         Spawn (); 
 
 
         }
 
 
     // Use this for initialization
     void Spawn () {
         int spawnPointsIndex = Random.Range (0, spawnPoints.Length);
         Instantiate (FallingObjects[Random.Range (0,4)], spawnPoints[spawnPointsIndex].position, spawnPoints[spawnPointsIndex].rotation);
 
         transform.Translate (Vector3.down * fallSpeed * Time.deltaTime);
         if (transform.position.y < 4)
                 
         InvokeRepeating ("Spawn", spawnTime, spawnTime);
 
     }
 
 
 }