# V3216. Unity Engine. Checking a field with a specific Unity Engine type for null may not work correctly due to implicit field initialization by the engine.

The analyzer has detected an unreliable `null` check for a field that can be initialized in the Unity inspector. It is unreliable because it uses an operator that does not have an overload to consider the specifics of Unity script code. Unity implicitly initializes fields in the inspector with a base value if their type is `UnityEngine.Object` or derived from it (except for the `MonoBehaviour` and `ScriptableObject` classes). This object is the equivalent to `null`, but the `?.`, `??`, `??=`, and `is` operators do not have such information and identify it as a common value.

Look at the following example:

    public class ActivateTrigger: MonoBehaviour
    {
      [SerializeField]
      GameObject _target;

      private void DoActivateTrigger()
      {
         var target = _target ?? gameObject;
        ....
      }
    }

In this case, if the `_target` value has not yet changed at runtime, the `??` check assumes `_target` is unequal to `null`, regardless of whether the field value has been assigned in the Unity inspector.

To fix it, use `==`, `!=`, or shorthand checks (`field` or `!field`) that consider Unity's specific behavior when compared to `null`.

The fixed code might look as follows:

    public class ActivateTrigger: MonoBehaviour
    {
      [SerializeField]
      GameObject _target;

      private void DoActivateTrigger()
      {
        var target = _target;

        if (target == null)
          target = gameObject;
        ....
      }
    }

Now to check `target` for `null`, the `==` operator is used instead of `??`. This operator is overridden to handle the special case described earlier (like `target != null`), ensuring the check works correctly in all scenarios.

This diagnostic is classified as:

CWE-754