Fetch Jira issues based on JQL and print details like Key, assignee and FixVersion

[Ganesh]

I want to fetch Jira issues using JQL and print the fields(Key, Assignee..) values with the loop. Need some examples to do this. 

I could print Jira key value, but other issue fields print only "null"

def jiraQuery = 'project = "Test" AND status="done"'
def testExecutionSearch = jiraJqlSearch jql: jiraQuery

if (testExecutionSearch != null){
def issues = testExecutionSearch.data.issues

for (def jiraIssue : issues){
def issueId = jiraIssue.key
def issueEmail = assignee.emailAddress
echo issueId
echo issueEmail
}
}