Possibility to treat the returned value of a custom function as IRI and not as string #48

Hi,
Thank you for that nice tool.

I am trying out the custom function feature as described in the README.
My current problem is that even if the function returns a url, as:

    functions: {
            'http://example.com/grel.ttl#getSexUrl': function (data) {
			if (data[0] == 1) {
				return `http://publications.europa.eu/resource/authority/human-sex/MALE`;
			} else {
				return `http://publications.europa.eu/resource/authority/human-sex/FEMALE`;
			}
                }
            },

But the generated RDF is:
<http://example.com/9791234567890> <http://data.europa.eu/m8g/sex> "http://publications.europa.eu/resource/authority/human-sex/FEMALE" .

What I want is a URL (and not a string) as object, for instance:
<http://example.com/9791234567890> <http://data.europa.eu/m8g/sex> <http://publications.europa.eu/resource/authority/human-sex/FEMALE> .

I am using the mapping as proposed in the README,

<#FunctionMap>
	fnml:functionValue [
		rml:logicalSource <#LOGICALSOURCE> ;
		rr:predicateObjectMap [
			rr:predicate fno:executes ;
			rr:objectMap [ 
				rr:constant grel:getSexUrl;
                                rr:termType rr:IRI
				]
		 ] ;
		rr:predicateObjectMap [
			rr:predicate grel:inputString ;
			rr:objectMap [ rml:reference "sex" ]
		 ];
	 ] .

I did also add a rr:termType rr:IR in the rr:objectMap (see here above), but same result.

I am no RML expert, and tried out quite a few things with no good result (even worse with the "help" of chatGPT)
Thank you for any pointer.
Fabian