minor fixes

openlp/plugins/songs/songsplugin.py

@@ -65,7 +65,7 @@ class SongsPlugin(Plugin):
         self.icon = build_icon(self.icon_path)
 
     def checkPreConditions(self):
-        return not self.manager.session == None
+        return self.manager.session is not None
 
     def initialise(self):
         log.info(u'Songs Initialising')

openlp/plugins/songusage/songusageplugin.py

@@ -54,6 +54,9 @@ class SongUsagePlugin(Plugin):
         self.inactiveIcon = build_icon(u':/songusage/song_usage_inactive.png')
         self.songUsageActive = False
 
+    def checkPreConditions(self):
+        return self.manager.session is not None
+
     def addToolsMenuItem(self, tools_menu):
         """
         Give the SongUsage plugin the opportunity to add items to the