---
title: MustBeNull
product: Unity Editor
version: '7000.0'
latest_version: '7000.0'
status: This page documents version 7000.0. The latest version is 7000.0.
canonical: https://docs.unity.com/en-us/engine/7000.0/script-reference/unityengine/assertions/must/mustextensions/mustbenull
latest_url: https://docs.unity.com/en-us/engine/7000.0/script-reference/unityengine/assertions/must/mustextensions/mustbenull.md
last_updated: 2026-10-07
generated_at: 2026-11-11T00:57:55.749Z
locale: en-us
---

# MustBeNull

> An extension method for Assert.IsNull.

## Definition

* **Type:** Method
* **Namespace:** [UnityEngine.Assertions.Must](/engine/7000.0/script-reference/unityengine/assertions/must.md)
* **Assembly:** UnityEngine.CoreModule

## MustBeNull\<T>(T)

An extension method for [Assert.IsNull](/engine/7000.0/script-reference/unityengine/assertions/assert/isnull.md).

> **Warning:**
>
> **Deprecated.** Must extensions are deprecated. Use UnityEngine.Assertions.Assert instead

```csharp
[Conditional("UNITY_ASSERTIONS")]
public static void MustBeNull<T>(this T expected) where T : class
```

### Parameters

**** (T):&#x20;

### Examples

```csharp
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.Assertions.Must;

public class AssertionExampleClass : MonoBehaviour
{
    MyClass myClassReference;
    void Update()
    {
        //Make sure the myClassReference reference is never set
        myClassReference.MustBeNull();
    }
}

public class MyClass {}
```

## MustBeNull\<T>(T, string)

An extension method for [Assert.IsNull](/engine/7000.0/script-reference/unityengine/assertions/assert/isnull.md).

> **Warning:**
>
> **Deprecated.** Must extensions are deprecated. Use UnityEngine.Assertions.Assert instead

```csharp
[Conditional("UNITY_ASSERTIONS")]
public static void MustBeNull<T>(this T expected, string message) where T : class
```

### Parameters

**** (T): **** (\[string]\(https\://learn.microsoft.com/dotnet/api/system.string)):&#x20;

### Examples

```csharp
using UnityEngine;
using UnityEngine.Assertions;
using UnityEngine.Assertions.Must;

public class AssertionExampleClass : MonoBehaviour
{
    MyClass myClassReference;
    void Update()
    {
        //Make sure the myClassReference reference is never set
        myClassReference.MustBeNull();
    }
}

public class MyClass {}
```