MissingComponentException: There is no component attached to the game object

Read the Console line first

X is the component type and Y is the GameObject name. Select that object and look for the component in the Inspector.

Common causes

1. The component is on a different object

   The Animator is on the child model, not on the root where the script lives, or the other way round.

2. 2D and 3D are mixed up

   The script asks for Rigidbody but the object has Rigidbody2D, or Collider when it has Collider2D. They are different components.

3. Animation and Animator are mixed up

   Animation is the legacy component; Animator is the one that plays Animator Controllers.

The fix

[RequireComponent(typeof(Rigidbody2D))]
public class Mover : MonoBehaviour
{
    private Rigidbody2D rb;

    void Awake() => rb = GetComponent<Rigidbody2D>();
}

Stop it coming back

[RequireComponent] makes Unity add the component when you attach the script and stops it from being removed. Every controller in this library that needs a Rigidbody declares it.

Questions

Why does a build show NullReferenceException for the same bug?

In the Editor, GetComponent returns a placeholder for a missing component that throws this exception and names the component and object. In a build it returns a real null, so you get a NullReferenceException instead. The fix is the same: add the component, or look for it on the right object.

How do I guarantee the component is always there?

Put [RequireComponent(typeof(Rigidbody))] above the class. Unity adds the component when the script is added and stops it being removed. It does not fix objects that already had the script before you added the attribute, so remove and re-add the script on those.

Should I use TryGetComponent instead?

Use TryGetComponent(out Rigidbody rb) when the component is optional, for example when a trigger may hit objects with or without health. It returns false instead of a placeholder, so you branch cleanly without an exception.

Scripts that avoid it

• 2D Player ControllerComplete 2D character controller with smooth movement, variable-height jumping, and coyote time.
• 3D Player ControllerFirst/third person character controller with smooth movement, jumping, and slope handling using CharacterController.

Related errors

• NullReferenceException: Object reference not set to an instance of an object
• MissingReferenceException: The object has been destroyed but you are still trying to access it
• UnassignedReferenceException: The variable has not been assigned
• IndexOutOfRangeException: Index was outside the bounds of the array
• ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection

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