ScriptRunner: set email address from custom field

Question

I am trying to dynamically set the recipient addresses based on the settings of a custom field ('Notification List', checkbox collection contains a list of department)

In the condition & configuration section, I have a

if ('Engineering' in cfValues['Notification List']*.value) {
recipients = recipients + ",addr1@host.com"
}
if ('Purchasing' in cfValues['Notification List']*.value) {
recipients = recipients + ",addr2@host.com"
}
mail.setTo(recipients)

So far so good, and working as expected

However, I'd like to pull from another custom field (ProjMgr) for one of the conditions

if ('Project Management' in cfValues['Notification List']*.value) {
    pm = com.atlassian.jira.component.ComponentAccessor.getCustomFieldManager().getCustomFieldObjectByName("ProjMgr")
    pmValue = issue.getCustomFieldValue(pm)
    recipients = recipients + "," + pmValue
}

ProjMgr is User Picker type.  In this case, I got the user id in pmvalue.  How can I find the user's email address to construct the recipients list?

Jackson Loong_sdi04s · Answer

pmValue returns "jackson.loong(jackson.loong)"
and 
user returns null

I ended up using the following codes segment and seems to work

if ('Project Management' in cfValues['Notification List']*.value) {
    def pm = customFieldManager.getCustomFieldObjectByName("ProjMgr")
    if (pm != null) {
        def pmValue = issue.getCustomFieldValue(pm)
        if (pmValue != null && !((String) pmValue).isEmpty()) {
            def mailbox = ((ApplicationUser) pmValue).getEmailAddress() 
            recipients = recipients + "," + mailbox            
        }
     }
}

JamieA · Answer

What does: "(String) pmValue " produce? Add some logging for that variable.

Basically no user can be found with that key.

Jackson Loong_sdi04s · Answer

Thanks Julian.

I got this error "Cannot invoke method getEmailAddress() on null object" when I tried to preview my codes.