Gotcha when testing Unity Objects for null in C#

Unity has overloaded the ‘==’ operator, specifically, checking objects against “null” might not always do what you expect. More information can be found in this blog post from Unity.

Specifically, if a Unity Object (as opposed to a C# object) gets destroyed, it will be set to a “fake null” object.  In this case, the following statements are true:

    obj == null          // true    obj is null          // false
    (object)obj == null  // false
    obj ?? value         // obj

Note the different results between lines 1 and  2 & 3.

If obj truly is null, then the results are as expected:

    obj == null          // true
    obj is null          // true
    (object)obj == null  // true
    obj ?? value         // value

It may be more readable to provide an Extension Method to UnityObject:

    /// <summary>
    /// Extension Method on Unity Objects returning whether the object really is null.
    /// </summary>
    /// Unity overloads the '==' operator so that it returns true on both null references
    /// as well as references to destroyed objects. This function only returns true if
    /// the reference truly is null, and returns false for "fake null" objects.
    public static bool IsTrueNull(this UnityEngine.Object ob)
        return (object)ob == null;