The issue is illustrated by this gist:

https://gist.github.com/anatoly-scherbakov/9fafb2863b877991f56ac7766b7c1bf0

• I use @base <local:> . in an RDF/N3 document, which should convert an RDF term <Category> to <local:Category>.
• But instead I get an error raised.
• If I try <local:/> instead as a @base — everything works.

But I was trying to get <local:> working, and also, I believe, <local:Category> is a perfectly good IRI. Real world examples of such schemas may be doi and mailto.

This might be related to #816 but I am not certain of that.

rdflib version is 5.0.0. The exception is raised here:

https://github.com/RDFLib/rdflib/blob/master/rdflib/plugins/parsers/notation3.py#L139-L144

I would be happy to create a PR removing this check, but I would like first to understand why the check is implemented.