Catch non existing environment variable

studsauger/studsauger.py

@@ -23,10 +23,12 @@ def main():
         else:
             print('Die Konfigurationsdatei "' + args.config + '" existiert nicht!')
             exit(1)
-    elif os.path.isfile(os.environ['XDG_CONFIG_HOME'] + '/studsauger/config.yaml'):
-        configpath = os.environ['XDG_CONFIG_HOME'] + '/studsauger/config.yaml'
-    elif os.path.isfile(os.environ['HOME'] + '/.config/studsauger/config.yaml'):
-        configpath = os.environ['HOME'] + '/.config/studsauger/config.yaml'
+    elif 'XDG_CONFIG_HOME' in os.environ:
+        if os.path.isfile(os.environ['XDG_CONFIG_HOME'] + '/studsauger/config.yaml'):
+            configpath = os.environ['XDG_CONFIG_HOME'] + '/studsauger/config.yaml'
+    elif 'HOME' in os.environ:
+        if os.path.isfile(os.environ['HOME'] + '/.config/studsauger/config.yaml'):
+            configpath = os.environ['HOME'] + '/.config/studsauger/config.yaml'
 
     if configpath:
         with open(configpath, 'r') as stream: