private void checkIllegalModifier(Modifier modifier) {
        if (method.getModifiers().contains(modifier)) {
          printMessage(ERROR, "@Memoized methods cannot be %s", modifier.toString());
        }
      }
The overriding method that should be added to the subclass.
value/src/main/java/com/google/auto/value/extension/memoized/processor/MemoizeExtension.java