fix config_files() so that it returns the correct values

Author: barryorourke

CHANGELOG.md

@@ -4,9 +4,11 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 This CHANGELOG follows the format listed [here](https://github.com/sensu-plugins/community/blob/master/HOW_WE_CHANGELOG.md)
 
 # [Unreleased]
+## Fixed
+- Fixes `utils.config_files` so that it returns a list of files, rather than a list of `None`'s (@barryorourke)
 
 # [0.4.2]
-##Fixed
+## Fixed
 - Fixes `client_name` in `bail()` as it was using an incorrect path within `event` dict (@absolutejam)
 
 # [0.4.1]

sensu_plugin/utils.py

@@ -20,9 +20,11 @@ def config_files():
         return sensu_config_files.split(':')
     else:
         files = ['/etc/sensu/config.json']
-        return [files.append('/etc/sensu/conf.d/{}'.format(filename))
-                for filename in os.listdir('/etc/sensu/conf.d')
-                if os.path.splitext(filename)[1] == '.json']
+        filenames = [f for f in os.listdir('/etc/sensu/conf.d')
+                     if os.path.splitext(f)[1] == 'json']
+        for filename in filenames:
+            files.append('/etc/sensu/conf.d/{}'.format(filename))
+        return files
 
 
 def get_settings():