Error in one_cell_minds jupyter notebook tutorial

**Describe the bug**
There's an error when running the jupyter notebook one_mind_cells when following the tutorial from this page: https://bluebrainnexus.io/docs/getting-started/try-nexus.html

**What part of Nexus is affected**
- [ ] Fusion
- [ ] Delta
- [ ] CLI
- [X] Documentation

**To Reproduce**
Steps to reproduce the behavior:
1. Go to: https://bluebrainnexus.io/docs/getting-started/try-nexus.html#2-6-running-the-notebook
2. Click on Google Colab or Binder (The problem happens in both)
3. Execute all cells until cell 11.
The content of the cell is:
``` forge =
KnowledgeGraphForge("https://raw.githubusercontent.com/BlueBrain/nexus/ef830192d4e7bb95f9351c4bdab7b0114c27e2f0/docs/src/main/paradox/docs/getting-started/notebooks/forge.yml",
bucket=f"{ORG}/{PROJECT}",
endpoint="https://sandbox.bluebrainnexus.io/v1",
token=TOKEN)
```

5. See error:
```
UnboundLocalError Traceback (most recent call last)
[](https://localhost:8080/#) in
----> 1 forge = KnowledgeGraphForge("https://raw.githubusercontent.com/BlueBrain/nexus/ef830192d4e7bb95f9351c4bdab7b0114c27e2f0/docs/src/main/paradox/docs/getting-started/notebooks/forge.yml",
2 bucket=f"{ORG}/{PROJECT}",
3 endpoint="https://sandbox.bluebrainnexus.io/v1",
4 token=TOKEN)

10 frames
[/usr/local/lib/python3.9/dist-packages/rdflib/plugins/shared/jsonld/context.py](https://localhost:8080/#) in _prep_sources(self, base, inputs, sources, referenced_contexts, in_source_url)
447 if isinstance(source, list):
448 self._prep_sources(
--> 449 new_base, source, sources, referenced_contexts, source_url
450 )
451 else:

UnboundLocalError: local variable 'new_base' referenced before assignment
```

**Expected behavior**
I expect the cell to run properly and be able to continue running the tutorial