wrappers: fixed locks for empty collection

it caused "Locks" checkbox to be checked, and it picked up first lock
from selectbox as default.

Change-Id: I13fdf104c6c32b783fb539f8947e3e071cb9788c
Signed-off-by: Lukas Bednar <lbednar@redhat.com>

jenkins_jobs/modules/wrappers.py

@@ -424,22 +424,21 @@ def locks(parser, xml_parent, data):
 
     :arg: list of locks to use
 
-    Example::
+    Example:
 
-      wrappers:
-        - locks:
-            - FOO
-            - FOO2
+    .. literalinclude::  /../../tests/wrappers/fixtures/locks002.yaml
+       :language: yaml
     """
-    lw = XML.SubElement(xml_parent,
-                        'hudson.plugins.locksandlatches.LockWrapper')
-    locktop = XML.SubElement(lw, 'locks')
     locks = data
-    for lock in locks:
-        lockwrapper = XML.SubElement(locktop,
-                                     'hudson.plugins.locksandlatches.'
-                                     'LockWrapper_-LockWaitConfig')
-        XML.SubElement(lockwrapper, 'name').text = lock
+    if locks:
+        lw = XML.SubElement(xml_parent,
+                            'hudson.plugins.locksandlatches.LockWrapper')
+        locktop = XML.SubElement(lw, 'locks')
+        for lock in locks:
+            lockwrapper = XML.SubElement(locktop,
+                                         'hudson.plugins.locksandlatches.'
+                                         'LockWrapper_-LockWaitConfig')
+            XML.SubElement(lockwrapper, 'name').text = lock
 
 
 def copy_to_slave(parser, xml_parent, data):

tests/wrappers/fixtures/locks001.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <buildWrappers/>
+</project>

tests/wrappers/fixtures/locks001.yaml

@@ -0,0 +1,2 @@
+wrappers:
+    - locks:

tests/wrappers/fixtures/locks002.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<project>
+  <buildWrappers>
+    <hudson.plugins.locksandlatches.LockWrapper>
+      <locks>
+        <hudson.plugins.locksandlatches.LockWrapper_-LockWaitConfig>
+          <name>FOO</name>
+        </hudson.plugins.locksandlatches.LockWrapper_-LockWaitConfig>
+        <hudson.plugins.locksandlatches.LockWrapper_-LockWaitConfig>
+          <name>FOO2</name>
+        </hudson.plugins.locksandlatches.LockWrapper_-LockWaitConfig>
+      </locks>
+    </hudson.plugins.locksandlatches.LockWrapper>
+  </buildWrappers>
+</project>

tests/wrappers/fixtures/locks002.yaml

@@ -0,0 +1,4 @@
+wrappers:
+    - locks:
+        - FOO
+        - FOO2