Unity AddComponent return null

I have a Monobehavior with or without a Rigidbody2D component. I want to get it or create it if needed.

The AddComponent, returns null on my game. Often, not every time, the log appeared.

Using:

• Unity 2019.2.19
• Android Platform

void Start()
{
    Rigidbody2D rb = gameObject.GetComponent<Rigidbody2D>() ?? 
        gameObject.AddComponent<Rigidbody2D>();

    if (rb == null)
    {
        Debug.LogError("No way to be here!");
    }
}

I can remove the ?? and do this in multiple lines, it doesn't change the error.

Do you have a solution to get the Rigidbody2D component?

I found the solution. The coalescing operator doesn't works with MonoBehavior and I need to get the Component a third time to make it work. It seems that the AddComponent does not work with Rigidbody2D.

This code works:

Rigidbody2D  rb = gameObject.GetComponent<Rigidbody2D>();

if (rb == null)
{
    rb = gameObject.AddComponent<Rigidbody2D>();
}

if (rb == null)
{
    rb = gameObject.GetComponent<Rigidbody2D>();
}