--- a/plcopen/plcopen.py	Mon Feb 19 19:10:07 2018 +0300
+++ b/plcopen/plcopen.py	Mon Feb 19 19:36:43 2018 +0300
@@ -441,7 +441,7 @@
                     "authorName": contentheader_obj.setauthor,
                     "pageSize": lambda v: contentheader_obj.setpageSize(*v),
                     "scaling": contentheader_obj.setscaling}.get(attr)
-            if func is not None:
+            if func is not None and value is not None:
                 func(value)
             elif attr in ["modificationDateTime", "organization", "language"]:
                 setattr(contentheader_obj, attr, value)