Minor Description
The SerializingObjectSizeOfStrategy.sizeof() method will return -1 in the case where it is unable to serialize the object (to determine its size). However, in those cases, the user is unaware that an accurate size could not be determined.
I think it would be beneficial for a warning to be logged in those cases, that way it still doesn't fail, but the developers can see when their expecations are not being met. I don't think a full stacktrace is warranted, but just the Exception message.