Unable to use rowCount() in Hibernate where-criteria

Question

I'm trying to create a simple query in Grails using Hibernate. I want to return the number of elements in each status. The query in sql looks like this:

select status, count(*) from UDTRAEKDATA
where UDTRAEK_JOB_ID='41'
group by status;

which produces the following table

STATUS	COUNT(*)
FAERDIG	12023
FEJL	434

The domain class is defined as follows:

class Udtraekdata {

    String jsonData
    UdtraekdataStatus status
    UdtraekEntitetType entitetType
    Date lastUpdated
    int antalLaasNulstillinger

    static hasOne = [udtraekdatafil: Udtraekdatafil, udtraekJob: UdtraekJob]

    static constraints = {
        udtraekdatafil nullable: true
        jsonData nullable: true
        faerdigbehandlet nullable: true
    }

    static mapping = {
        status index: 'idx_udtraekdata'
        udtraekJob index: 'idx_udtraekdata'
        udtraekdatafil index: 'Udtraekdata_fil_idx'
        id generator: 'sequence', params:[sequence: 'udtraekdata_sequence']
    }

}

I believe I should be able to create the corresponding query in Hibernate like this (Done here f.ex. grails 3.3 gorm where query with projection count() different than list().size()):

    Udtraekdata.where {
            udtraekJob.jobId == "job1"

            projections {
                groupProperty 'status'
                rowCount()
            }
        }.list()

However this resulst in a GroovyCastException with the message:

"Cannot cast object '10' with class 'java.lang.Integer' to class 'java.util.List'"

What am I missing? I want to do this lazily, as there will be millions of rows and I don't ever want to fetch them into memory.