Showcase How to solve Android error: no static method with name='loadBanner'

In case anyone has got this error:

Code (csharp):

1. unity android Error Unity java.lang.NoSuchMethodError: no static method with name='loadBanner' signature='(Lcom.unity3d.player.UnityPlayerActivity;)V' in class Ljava.lang.Object;

Make sure your placementId is NOT null. The c# API has a method for placementId = null but the java side does not. A likely cause is a timing problem (calling load before the placementId is set).

Observed in Unity 2021.3.26f1 with Advertisement Legacy 4.4.2

Spoiler

This code tries to call a non-existent java method if placementId is null:

Code (CSharp):

1. if (placementId != null)
2. {
3.     m_BannersClass.CallStatic("loadBanner", m_CurrentActivity, placementId);
4. }
5. else
6. {
7.     m_BannersClass.CallStatic("loadBanner", m_CurrentActivity); // This will always FAIL because there is no java method for this.
8. }

No such method in the java source. I guess no one ever tested it with a null placement id.

My understand is that all of this is now legacy code and no fix will be done. May it help others who (like me) have not yet upgraded.