If you use code such as "def list = new ArrayList(); print(list.size)" it will produce the warning within the Java9 class, where the field lookup is performed.
The solution to this from your perspective is to use the size method, aka "list.size()". If you suspect such field usage exists within the Groovy runtime, it would be helpful to find it so we can make a similar change. We do have one or two test cases that do this on purpose to exercise the warning.
