RigidBody MotionEnabled defaults to false if not serialized

[yuberee]

Describe the bug

Many of our prefabs don't have MotionEnabled serialized, which has always worked because it defaults to true, so I guess it never needed to in the first place.
But as of recently, if MotionEnabled isn't serialized it defaults to false.

To Reproduce

Here's an example of a prefab missing the MotionEnabled property:
split_wooden_log.json
(Rename the type from .json to .prefab, it doesn't let me upload those)

When opening it in the editor, you'll see that MotionEnabled is false.

Expected behavior

MotionEnabled is true by default, it should be true when missing while deserializing.

Media/Files

Example of bug found recently because of the change.

sbox.2024.12.18.23.06.18.mp4

Additional context

The fix on our part is easy, just reenable and save. But who knows what else it broke.

[aylaylay]

This was an unfortunate oversight when changing json to serialize defaults. I can't think of a nice way to automatically fix right now.