Simple REST endpoint and fragment not working Script function failed on issue: issue: PIE-68635, user: mouh, fieldId: __init__, file: <inline script>

I am using a really simple REST endpoint and its corresponding fragment and it is not working for me. 

The fragment I created is the following: 

Here is the error that I get printed in the log: 

2022-08-17 00:00:40,405+0200 https-openssl-nio-443-exec-297 ERROR mouh 0x69166x26 nxp314 10.248.27.109 /rest/scriptrunner/behaviours/latest/validators.json [c.o.jira.behaviours.BehaviourManagerImpl] Script function failed on issue: issue: PIE-68635, user: mouh, fieldId: __init__, file: <inline script>, edit behaviour: https://itrac-dev.eur.ad.sag/plugins/servlet/scriptrunner/admin/behaviours/edit/15, https://itrac-dev.eur.ad.sag/plugins/servlet/scriptrunner/admin/behaviours/edit/17, https://itrac-dev.eur.ad.sag/plugins/servlet/scriptrunner/admin/behaviours/edit/21
2022-08-17 00:00:40,405+0200 https-openssl-nio-443-exec-297 ERROR mouh 0x69166x26 nxp314 10.248.27.109 /rest/scriptrunner/behaviours/latest/validators.json [c.o.jira.behaviours.BehaviourManagerImpl]

Here is the code for the REST endpoint, the code is super simple as you can tell:

import com.onresolve.scriptrunner.runner.rest.common.CustomEndpointDelegate

import groovy.json.JsonBuilder

import groovy.transform.BaseScript

import javax.ws.rs.core.MultivaluedMap

import javax.ws.rs.core.Response

@BaseScript CustomEndpointDelegate delegate

callMounaSubTaskCreator( 

    httpMethod: "GET", groups: ["jira-administrators"] 

) { MultivaluedMap queryParams, String body -> 

    return Response.ok(new JsonBuilder([abc: 42]).toString()).build() 

}