The email publisher needs a list of recipients

The email publisher will throw a NullPointerException of the recipients
xml element does not exist, so if there are no recipients then set the
value to an empty string in order to get an empty xml element in the
config.

Also add tests for the email publisher.

story: 2000015
Change-Id: I7b4fdd4904eea1918ae80f5db6c7b0aaedbaef99

jenkins_jobs/modules/publishers.py

@@ -1298,18 +1298,16 @@ def email(parser, xml_parent, data):
     :arg bool send-to-individuals: Send an email to the individual
       who broke the build (default false)
 
-    Example::
+    Example:
 
-      publishers:
-        - email:
-            recipients: breakage@example.com
+    .. literalinclude::  /../../tests/publishers/fixtures/email001.yaml
+       :language: yaml
     """
 
     # TODO: raise exception if this is applied to a maven job
     mailer = XML.SubElement(xml_parent,
                             'hudson.tasks.Mailer')
-    if 'recipients' in data:
-        XML.SubElement(mailer, 'recipients').text = data['recipients']
+    XML.SubElement(mailer, 'recipients').text = data.get('recipients', '')
 
     # Note the logic reversal (included here to match the GUI
     if data.get('notify-every-unstable-build', True):

tests/publishers/fixtures/email001.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <publishers>
+    <hudson.tasks.Mailer>
+      <recipients>foo@example.com bar@example.com</recipients>
+      <dontNotifyEveryUnstableBuild>false</dontNotifyEveryUnstableBuild>
+      <sendToIndividuals>false</sendToIndividuals>
+    </hudson.tasks.Mailer>
+  </publishers>
+</project>

tests/publishers/fixtures/email001.yaml

@@ -0,0 +1,3 @@
+publishers:
+  - email:
+      recipients: foo@example.com bar@example.com

tests/publishers/fixtures/email002.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <publishers>
+    <hudson.tasks.Mailer>
+      <recipients/>
+      <dontNotifyEveryUnstableBuild>false</dontNotifyEveryUnstableBuild>
+      <sendToIndividuals>true</sendToIndividuals>
+    </hudson.tasks.Mailer>
+  </publishers>
+</project>

tests/publishers/fixtures/email002.yaml

@@ -0,0 +1,4 @@
+publishers:
+  - email:
+      send-to-individuals: true
+