DX for ledger creation

[flyingmachine]

If you create a ledger with an empty txn:

{
    "ledger": "example-ledger",
    "txn": {}
}

And then transact data:

{
    "ledger": "example-ledger",
    "txn": {"name": "Derek"}
}

The response includes an error with the message "Commit has neither assertions or retractions!".

I found this to be confusing and have some concerns:

• I wonder if an endpoint path like /create-ledger or /ledger/create might be clearer?
• The API request to create the ledger "succeeded" in that a success response was returned and a ledger was actually created. This led me to believe it was ok to continue using the ledger
• There's a large distance between the text of the error message and the underlying problem, and there's no suggestion for how to solve the issue
• There's also a large distance between the source of the error and the point in the workflow where it shows up. The error came up when transacting new data, which led me to believe that the problem was with the data I was transacting. It's unobvious that the problem is related to the state management of a previous step
• The necessity to include a txn in ledger creation seems to come solely from the need to satisfy some internal implementation details of Fluree, and I don't think we should make it the user's responsibility to do this
• If we do make the user do this, it's hard to explain why it's necessary, and again burdens them with having to learn things they ideally shouldn't have to learn
• I can imagine users including junk data in the initial txn so that they can satisfy this requirement, and I don't think that we should create a scenario where we're encouraging users to include junk data
• In general I don't see how having to include txn on ledger creation helps users get their work done

[mpoffald]

@flyingmachine Sorry, I just now saw this when browsing issues. We implemented a change recently to disallow persisting empty transactions (or transactions that have just an @id, which is insufficient) in the first place (issue: https://github.com/fluree/db/issues/402, PR: https://github.com/fluree/db/pull/407).

[mpoffald]

I realize this does not address all of this feedback, but I wanted to make you aware of the change in case you weren't already. A user attempting to create a ledger with an empty transaction will now get an error like "Invalid transaction, transaction node contains no properties for: @id: http://example.org/ns/someone".

So they will at least receive that error when they attempt it in the first place, instead of getting a misleading success response and then getting a confusing error the next time they interact with the ledger.