GbpConfArgParser.get_conf_file_value: only allow valid options

Raise an exception if the queried option is not in the list of valid
config file args.

Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>

gbp/config.py

@@ -702,10 +702,10 @@ def get_conf_file_value(self, option_name):
         @returns: The config file option value or C{None} if it doesn't exist
         @rtype: C{str} or C{None}
         """
-        try:
+        if option_name in self.conf_file_args:
             return self.config.get_value(option_name)
-        except KeyError:
-            return None
+        else:
+            raise KeyError("Invalid option: %s" % option_name)
 
 
 class GbpConfigDebian(GbpConfig):

tests/18_test_Config.py

@@ -95,9 +95,11 @@ def test_get_conf_file_value(self):
         Read a single value from the parsed config
         """
         parser = GbpConfArgParser.create_parser(prog='cmd4')
+        parser.add_conf_file_arg('--new_overrides_git_option1')
         self.assertEqual(parser.get_conf_file_value('new_overrides_git_option1'),
                          'new_overrides_git_value1')
-        self.assertEqual(parser.get_conf_file_value('doesnotexist'), None)
+        with self.assertRaises(KeyError):
+            parser.get_conf_file_value('doesnotexist')
 
     def test_param_list(self):
         parser = GbpConfArgParser.create_parser(prog='cmd4')