[common] check that VISUAL or EDITOR is set in the environment

beat/cmdline/common.py

@@ -575,9 +575,9 @@ def edit_local_file(prefix, editor, type, name):
     if os.path.isfile(object_path):
         # check if editor set
         if editor is None:
-          if len(os.environ['VISUAL']) > 0:
+          if 'VISUAL' in os.environ and len(os.environ['VISUAL']) > 0:
             editor = os.environ['VISUAL']
-          elif len(os.environ['EDITOR']) > 0:
+          elif 'EDITOR' in os.environ and len(os.environ['EDITOR']) > 0:
             editor = os.environ['EDITOR']
           else:
             logger.error("No default editor set in your environment variable")