Firestore set() with {merge: true} does not merge empty objects

[merlinnot]

• Operating System version: any
• Firebase SDK version: 6.0.0
• Library version: _____
• Firebase Product: Firestore

Steps to reproduce:

Behaviour is exactly the same as described in firebase/firebase-js-sdk#1168, tested using transactions.

To reproduce, set any document to { data: { "i-am": "important" } } and run the code below in a transaction. data will be set to an empty object. Didn't test it with simple set.

Relevant Code:

transaction.set(documentReference, { data: {} }, { merge: true })

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[wilhuff]

Sorry for the delay in resolving this, but upon review we believe this is working correctly, and consistently with the other SDKs.

See commentary here: firebase/firebase-js-sdk#1371 (comment).