keep copyright field empty if imported song does not have any copyright information

openlp/core/lib/serviceitem.py

@@ -44,6 +44,7 @@ class ServiceItemType(object):
     Image = 2
     Command = 3
 
+
 class ItemCapabilities(object):
     """
     Provides an enumeration of a serviceitem's capabilities

openlp/plugins/songs/lib/xml.py

@@ -297,6 +297,8 @@ class OpenLyricsParser(object):
         song_xml = objectify.fromstring(xml)
         properties = song_xml.properties
         song.copyright = unicode(properties.copyright.text)
+        if song.copyright == u'None':
+            song.copyright = u''
         song.verse_order = unicode(properties.verseOrder.text)
         if song.verse_order == u'None':
             song.verse_order = u''