docs: public static void setInvocationHandler(Object instance, InvocationHandler handler) {
          try {
              Field handlerField = instance.getClass().getDeclaredField(FIELD_NAME_HANDLER);
              handlerField.setAccessible(true);
              handlerField.set(instance, handler);
          } catch (NoSuchFieldException e) {
              throw new IllegalArgumentException("Not a valid proxy instance", e);
          } catch (IllegalAccessException e) {
              // Should not be thrown, we just set the field to accessible.
              throw new AssertionError(e);
          }
      }