Ambiguous method overloading for method ApplicationUsers#from

unknown

Recently we upgraded to JIRA 6.3.15 and ScriptRunner v3 and one of the our Scripted Fields does not work anymor.  The log file records the following error:

groovy.lang.GroovyRuntimeException: Ambiguous method overloading for method com.atlassian.jira.user.ApplicationUsers#from.
Cannot resolve which method to invoke for [null] due to overlapping prototypes between:
[interface com.atlassian.crowd.embedded.api.User]
[interface java.util.Collection]

It was working just fine previously in JIRA 5.  I'm aware of a change in ApplicationUser interface in JIRA 6 but just wondering if the problem lies with my script or the fact that the use of this interface has been changed since the upgrade?

My script is just a simple script that collects user from customfields:

Collection<ApplicationUser> appUserCollection = []

appUserCollection.add(ApplicationUsers.from(issue.getCustomFieldValue(CustomFieldObject)))

unknown

Hi Jamie, Thanks for the pointer. We handled the null value by adding '?' operator when getting the custom field value. However what we found is that your suggestion still returns the same error. We tried different permutations such as below (enforce it in one level before):

appUserCollection.add(ApplicationUsers.from(issue.getCustomFieldValue(CustomFieldObject)) as ApplicationUser)

But still received the same error. If I enforce it at the lowest level like this:

appUserCollection.add(ApplicationUsers.from(issue.getCustomFieldValue(CustomFieldObject) as ApplicationUser))

We will get

'No signature of method: static com.atlassian.jira.user.ApplicationUsers.from() is applicable for argument types: (null) values: [null]'.

What we found to be working is to enforce it as User when the ApplicationUsers is calling the 'from' method:

appUserCollection.add(ApplicationUsers.from(issue.getCustomFieldValue(CustomFieldObject) as User))

as this will feed User type to ApplicationUsers and return a single User. Hope this can help others.