Accessing Nested Array Without .get() Adds Empty Object to Change Object

## Version

3.13.6

## Steps to reproduce

1. Create a Changeset (from Ember-Data object in my case) with a nested array:
`{ name: "Example, address: { residentIds: ["abc123"] } }`
2. Access the nested array in Javascript :
`const residentIds = changeset.address.residentIds`
3. Edit any other (non-object) attribute value

## Expected Behavior

The change {} object and the changes [] array on the changeset should be uneffected:
`changeset: {
changes: [],
change: {}
}`

## Actual Behavior

The change {} object on the changeset has an empty value for the high-level key ("address" in above example), and changes [] array does not reflect it:
`changeset: {
changes: [],
change: {
address: {}
}
}`

**If you use .get() syntax, this behavior does not occur: `const residentIds = changeset.get('address.residentIds')`**