Damn Compiler Errors, pls help me

Greetings Fellow Developers,

I'm constructing a Game for a Project which requires me to spawn in random blocks (or Prefabs to use technical terms) on the end of the map so they spawn a random Block each time, which in effect makes an endless map.

It all worked fine until I followed the tutorial section which Randomises the Blocks (prefabs being Spawned). The Compiler Error says: not all code paths return a value.

The code is as follows: using System.Collections; using System.Collections.Generic; using UnityEngine;

public class BlockManager : MonoBehaviour { //Creating a GameObject to drag-and-drop BlockPrefabs into for use. public GameObject[] blockPrefabs;

 //declaring variables for use in the Script
 private Transform playerTransform;
 //distance behind the character where blocks are spawned
 private float spawnZAxis = -10.0f;
 //The length of the blocks being used in the Script/Game
 private float blockLength = 50.0f;
 //default amount of blocks on the screen
 private int amnBlocks = 4;
 //Records the first block used so a blank one will never be spawned in again
 private int lastBlockUsed = 0;
 //This section finds the Player Object and acquires it's position, from there, it then spawns a block for the Game Character. 
 void Start()
 {
     //Assigning the List to the Variable
     //activeBlocks = new List<GameObject>();
     playerTransform = GameObject.FindGameObjectWithTag("PlayerObject").transform;
     //Here shall detect when the Player moves a certain distance and then calls the functions to make a Block and Delete the End one.
     for (int i = 0; i < amnBlocks; i++)
     {
         SpawnBlock();
         //DeleteBlock(); 
     }
 }

 // Update is called once per frame. Thos will call the SpawnBlock Function when the player moves along a certain distance on the game.
 void Update()
 {
     if (playerTransform.position.z > (spawnZAxis - amnBlocks * blockLength))
     {
         SpawnBlock();
     }
 }

 private void SpawnBlock(int prefabIndex = -1)
 {
     GameObject go;

     go = Instantiate(blockPrefabs [RandomBlock()]) as GameObject;
     go.transform.SetParent(transform);
     go.transform.position = Vector3.forward * spawnZAxis;
     spawnZAxis += blockLength; 
 }

 private int RandomBlock()
 {
     if (blockPrefabs.Length <= 1)
         return 0;
     
     int randomInt = lastBlockUsed;
     while(randomInt == lastBlockUsed)
     {
         randomInt = Random.Range(0, blockPrefabs.Length);
     }
 }

} The Issue is the private int RandomBlock() Section towards the bottom which it doesn't like?

I'm stumped. I'm an absolute noob at Unity so a solution to this would be Gucci!

Thanks in advance Fellow Developers,

C