Set a multi group picker custom field via a post function

Problem:

If you want to set a "Group Picker (multiple groups)" with a post-function.

If a "customer" makes a new Task, the Group Picker "Security Level Group" should be automatically filled with the existing Group "customer".

the following if/else works, and I can set the Description depending on customer yes/no, but i have no Chance to set the customer-group into my userSecGrp.

I also did not find anything in the Internet that could help me.

def userSecGrp = customFieldManager.getCustomFieldObjectByName("Security Level Group")

def groupManager = ComponentAccessor.getGroupManager()
if (groupManager.isUserInGroup(issue.reporter?.name, 'customer') ) {
    issue.setDescription("A generated description for extern customer") 
    def group = groupManager.getGroup("customer")
    def groupObj = groupManager.getGroupObject('customer')
    
   // issue.setCustomFieldValue(userSecGrp, group)    
    //issue.setCustomFieldValue(userSecGrp, group)     //issue.setCustomFieldValue(userSecGrp, groupManager.getGroupObject('customer'))     //issue.setCustomFieldValue(userSecGrp, userUtil.getUserByName("eninaus")) } else {
  // system fields   issue.setDescription("A generated description for non-customer")
}

If i activate one of the setCustomFieldValue, I only get the message that something is not compatible to my jira Version.

So the question is: How to setCustomFieldValue for a Group Picker to a Group? or GroupObject...

Thx for your support

Solution

The following code works for me to set the value of single and multigroup custom fields:

import com.atlassian.jira.component.ComponentAccessor

def customFieldManager = ComponentAccessor.getCustomFieldManager()
def groupManager = ComponentAccessor.getGroupManager()

def multiGroupCf = customFieldManager.getCustomFieldObjectByName("multigrouppicker")
def singleGroupCf = customFieldManager.getCustomFieldObjectByName("GroupPicker")

def group = groupManager.getGroup("jira-developers")

issue.setCustomFieldValue(multiGroupCf, [group])
issue.setCustomFieldValue(singleGroupCf, [group])