The prefab is assigned on the prefab asset. Why is it null in the scene?

The scene instance can override the field. Select the object in the Hierarchy and check the slot there; a bold field means an override. Revert the override, or assign the prefab on the instance.

Why does Resources.Load return null?

The asset must sit inside a folder named Resources, and the path you pass is relative to that folder, without the file extension: Resources.Load ("Enemies/Goblin") for Assets/Resources/Enemies/Goblin.prefab. Check the spelling and case.

Is there a better way than Resources?

For larger projects, Addressables load assets by address asynchronously and keep them out of the initial build. For a few prefabs, a serialized field on a component is simplest and fails visibly in the Inspector when empty.

ArgumentException: The Object you want to instantiate is null

ConsoleRuntime exception · Prefabs

ArgumentException: The Object you want to instantiate is null.

Instantiate was given null instead of a prefab or object to copy. Older Unity versions word it as: The thing you want to instantiate is null.

Read the Console line first

The stack trace names the Instantiate call. Check the variable passed as its first argument.

Common causes

The prefab field is empty

The script's prefab slot shows None in the Inspector. Drag the prefab asset from the Project window into it.
Resources.Load returned null

The path is wrong, the asset is not inside a folder named Resources, or the path includes the file extension, which it must not.
The template was a scene object that got destroyed

Cloning an object from the scene works until that object is destroyed. Use a prefab asset as the template instead.

The fix

 Fix
C# 
 [SerializeField] private GameObject bulletPrefab;

void Fire()
{
    if (bulletPrefab == null)
    {
        Debug.LogError("Assign Bullet Prefab in the Inspector", this);
        return;
    }
    Instantiate(bulletPrefab, muzzle.position, muzzle.rotation);
}
 11 lines

Stop it coming back

Reference prefabs through serialized fields instead of Resources.Load strings, so a missing one is visible in the Inspector.

Questions

The prefab is assigned on the prefab asset. Why is it null in the scene?: The scene instance can override the field. Select the object in the Hierarchy and check the slot there; a bold field means an override. Revert the override, or assign the prefab on the instance.
Why does Resources.Load return null?: The asset must sit inside a folder named Resources, and the path you pass is relative to that folder, without the file extension: Resources.Load<GameObject>("Enemies/Goblin") for Assets/Resources/Enemies/Goblin.prefab. Check the spelling and case.
Is there a better way than Resources?: For larger projects, Addressables load assets by address asynchronously and keep them out of the initial build. For a few prefabs, a serialized field on a component is simplest and fails visibly in the Inspector when empty.

Scripts that avoid it

Related errors

Got a different error? Paste it into the error lookup.