Dataset adds graph labels where there were none

[sdasda7777]

If you run the following code

from rdflib import Dataset

input_data = "<http://s> <http://v> <http://o>."
ds = Dataset()
ds.parse(data=input_data, format="nquads")
print(ds.serialize(format="nquads"))

you will get something like <http://s> <http://v> <http://o> _:Nf7773353eb67460ab92041894df76998 .

I believe that is wrong, since there was no graph label in the input data, and RDF standard clearly distinguishes between the default graph and named graphs.

Is this a bug, or is there a way to make it not do that? If it is necessary to have some graph in there internally, I think I saw some tools use specific IRIs like http://www.w3.org/1999/02/22-rdf-syntax-ns#defaultGraph, but in that case there wouldn't be a reason not to leave those out when serializing.

[sdasda7777]

Actually, I managed to get the default graph data serialized with <urn:x-rdflib:default> graph label just now. I think the difference was I didn't use .parse(), but rather entered the data in myself 🤔

[aucampia]

This is essentially the same as this issue:

• rdfpipe adds a graph name to triples in the default graph, consequently breaking round tripping #1804

[aucampia]

Fix is more or less ready, please have a look:

• BREAKING CHANGE: Don't use publicID as the name for the default graph. #2406