Dynamic number of parallel steps in declarative pipeline

I'm trying to create a declarative pipeline which does a number (configurable via parameter) jobs in parallel, but I'm having trouble with the parallel part.

Basically, for some reason the below pipeline generates the error

 Nothing to execute within stage "Testing" @ line .., column ..

and I cannot figure out why, or how to solve it.

import groovy.transform.Field
@Field def mayFinish = false

def getJob() {
    return {
        lock("finiteResource") {
            waitUntil {
                script {
                    mayFinish
                }
            }
        }
    }
}

def getFinalJob() {
    return {
        waitUntil {
            script {
                try {
                    echo "Start Job"
                    sleep 3 // Replace with something that might fail.
                    echo "Finished running"
                    mayFinish = true
                    true
                } catch (Exception e) {
                    echo e.toString()
                    echo "Failed :("
                }
            }
        }
    }
}

def getJobs(def NUM_JOBS) {
    def jobs = [:]
    for (int i = 0; i < (NUM_JOBS as Integer); i++) {
        jobs["job{i}"] = getJob()
    }
    jobs["finalJob"] = getFinalJob()
    return jobs
}

pipeline {
    agent any
    options {
        buildDiscarder(logRotator(numToKeepStr:'5'))
    }
    parameters {
        string(
            name: "NUM_JOBS",
            description: "Set how many jobs to run in parallel"
        )
    }
    stages {
        stage('Setup') {
            steps {
                echo "Setting it up..."
            }
        }
        stage('Testing') {
            steps {
                parallel getJobs(params.NUM_JOBS)
            }
        }
    }
}

I've seen plenty of examples doing this in the old pipeline, but not declarative. Anyone know what I'm doing wrong?