workflow: ignore empty items on workflow import (#31823)

tests/test_workflow_import.py

@@ -568,7 +568,7 @@ def test_sms(pub):
     st1 = wf.add_status('Status1', 'st1')
 
     sendsms = SendSMSWorkflowStatusItem()
-    sendsms.to = ['0123456789']
+    sendsms.to = ['0123456789', '']
     sendsms.body = 'hello'
     st1.items.append(sendsms)
     sendsms.parent = st1

wcs/workflows.py

@@ -832,7 +832,7 @@ class XmlSerialisable(object):
                 continue
             if list(el):
                 if type(getattr(self, attribute)) is list:
-                    v = [x.text.encode(charset) for x in el]
+                    v = [x.text.encode(charset) if x.text is not None else '' for x in el]
                 elif type(getattr(self, attribute)) is dict:
                     v = {}
                     for e in el: