removed superfluous default

sani.py

@@ -15,7 +15,7 @@ def handle_clargs():
 
     parser_check = subparsers.add_parser("check", help="check a list of channels", formatter_class=argparse.ArgumentDefaultsHelpFormatter)
     parser_check.add_argument("filename", help="name of input channel-list file")
-    parser_check.add_argument("-o", "--output", help="output CSV file", default=None)
+    parser_check.add_argument("-o", "--output", help="output CSV file")
     parser_check.add_argument("-q", "--quiet", help="do not show each channel's answer", action="store_true")
     parser_check.add_argument("-s", "--serial", help="do not run checks in parallel", action="store_true")
     parser_check.add_argument("-t", "--timeout", help="connection timeout in seconds", type=float, default=1)