Merge pull request #66 from ecederstrand/patch-1

Pull in upstream commit 2dc1dee

exchangelib/properties.py

@@ -647,15 +647,17 @@ class FreeBusyView(EWSElement):
     @classmethod
     def from_xml(cls, elem, account):
         kwargs = {}
+        working_hours_elem = elem.find('{%s}WorkingHours' % TNS)
         for f in cls.FIELDS:
             if f.name == 'working_hours':
-                kwargs[f.name] = f.from_xml(elem=elem.find('{%s}WorkingHours' % TNS), account=account)
+                if working_hours_elem is None:
+                    continue
+                kwargs[f.name] = f.from_xml(elem=working_hours_elem, account=account)
                 continue
             kwargs[f.name] = f.from_xml(elem=elem, account=account)
         elem.clear()
         return cls(**kwargs)
 
-
 class RoomList(Mailbox):
     # MSDN: https://msdn.microsoft.com/en-us/library/office/dd899514(v=exchg.150).aspx
     ELEMENT_NAME = 'RoomList'