Deal with empty ccli tag in OpenSong imports

openlp/plugins/songs/lib/opensongimport.py

@@ -163,7 +163,10 @@ class OpenSongImport(SongImport):
                 ustring = str(root.__getattr__(attr))
                 if isinstance(fn_or_string, str):
                     if attr in ['ccli']:
-                        setattr(self, fn_or_string, int(ustring))
+                        if ustring:
+                            setattr(self, fn_or_string, int(ustring))
+                        else:
+                            setattr(self, fn_or_string, None)
                     else:
                         setattr(self, fn_or_string, ustring)
                 else:

tests/resources/opensongsongs/One, Two, Three, Four, Five

@@ -5,6 +5,7 @@
   <copyright>Public Domain </copyright>
   <presentation>T</presentation>
   <capo print="false"></capo>
+  <ccli></ccli>
   <tempo></tempo>
   <theme></theme>
   <alttheme></alttheme>