How to get all issues of a certain project and then group those issues by Organizations

[Enkhtaivan Ganbat]

I'm trying to get all issues of our service desk project and group the result by Organizations. I'm trying to do it by running the below script on ScriptRunner console.

Map<String, Object> searchResult = get('/rest/api/2/search')
.queryString('jql', 'project = "ITZone Software Support"')
.queryString('fields', '*all,-comment')
.queryString('maxResults', '1000')
.asObject(Map)
.body

def issues = (List<Map<String, Object>>) searchResult.issues

issues.groupBy { issue ->
((Map<String, Map>) issue.fields).Organizations
}.collectEntries { Organizations, issueList ->
[(Organizations): issueList.size()]
}.toString()

The result I'm getting is:

[null:100]

What went wrong in my script?