How to set up the ID of a json element in rdflib

Context

I am loading a rdf file in rdflib, and am trying to export it in json-ld.

The original rdf looks like:

<cim:Substation rdf:ID="_1234">
    <cim:IdentifiedObject.name>A substation</cim:IdentifiedObject.name>
</cim:Substation>

The exported json-lib looks like:

{
  "@id": "file:///path/to/original/xml#_418866779",
  "@type": "cim:Substation",
  "cim:IdentifiedObject.name": "A substation"
},

I cannot seem to override the file:///path/to/original/xml component in json.

Code

This is what I am doing:

from rdflib import Graph

g = Graph(
    # Giving an identifier or base does not seem to change anything
)
g.parse('path to rdf')
js = g.serialize(
    format="json-ld",
    encoding="utf-8",
    destination='path to json',
    sort_keys=True,  # repeatable output is Good.
    context={ some relevant entries (rdf, cim)  },
    auto_compact=True,
    # giving base does not seem to change anything
)

Question
How can I set/override the first component of the ID in the exported json-ld?

The solution was in the parse method, with the parameter publicID which is decribed in the source.

> the logical URI to use as the document base. If None
specified the document location is used (at least in the case where
there is a document location).

So my example in the question becomes

g.parse('path to rdf', publicID="#")

and the rest stays as is.