Empty datatype for override?

Richard-

I notice section 10.4 of the R2RML spec [1] says:

"The datatype-override RDF literal corresponding to a SQL data value
*v*and a (possibly empty) datatype
IRI <http://www.w3.org/2001/sw/rdb2rdf/r2rml/#dfn-datatype-iri> *dt"

*I am unable to think of a scenario where the datatype IRI would be empty
and there would still be a datatype-override condition. Can you explain
this?

Thank you.
-David