Getting error when trying to get missing field

Hello! I was trying to get a missing field of a message and expected to receive a undefind, but got an error saying `TypeError: Cannot read properties of null (reading '10')` (number for corresponding field).
Turned out that the problem occurred because wrappers_ field of the message was equal to null. In the jspb.Message.getWrapperField there is check to prevent it, looking like `a.wrappers_ || (a.wrappers_ = {});`. But for some strange reason that doesn't work and assignment left wrapper_ filed with null (I was trying to make it by myself before calling getMyField, it still didn't help).

I receive the "invalid" message from server, thats why wrappers_ set to null (if I create it with `new MyMessage` wrappers_ is set to {} and everything works fine)