Use None instead of string 'None'

Two command line options use the string 'None' instead of the
native type None as the default value.

This PR changes this.

updatesnap/SnapVersionModule/snap_version_module.py

@@ -88,7 +88,7 @@ def process_rock_version_data(upstream_version, previous_version, version_schema
 def is_version_update(snap, manager_yaml, arguments, has_update):
     """ Returns if snap version update available """
     has_version_update = False
-    if arguments.version_schema == 'None':
+    if arguments.version_schema is None:
         return False
     metadata = snap.process_metadata()
     if process_snap_version_data(metadata['upstream-version'], metadata['name'],
@@ -115,7 +115,7 @@ def is_version_update(snap, manager_yaml, arguments, has_update):
 def is_rock_version_update(rock, manager_yaml, arguments, has_update):
     """ Returns if rock version update available """
     has_version_update = False
-    if arguments.rock_version_schema == 'None':
+    if arguments.rock_version_schema is None:
         return False
     metadata = rock.process_metadata()
     rock_version = process_rock_version_data(metadata['upstream-version'], metadata['version'],

updatesnap/updatesnapyaml.py

@@ -79,9 +79,9 @@ def main():
                         help='User name for accessing Github projects.')
     parser.add_argument('--github-token', action='store', default=None,
                         help='Access token for accessing Github projects.')
-    parser.add_argument('--version-schema', action='store', default='None',
+    parser.add_argument('--version-schema', action='store', default=None,
                         help='Version schema of snapping repository')
-    parser.add_argument('--rock-version-schema', action='store', default='None',
+    parser.add_argument('--rock-version-schema', action='store', default=None,
                         help='Version schema of rock repository')
     parser.add_argument('--yaml-path', action='store', default=None,
                         help='Path to the yaml file')