PHP Notice: Undefined index: SERVER_NAME

Hi.

I am using Count Per Day Version 3.5.6. It seems to work fine but it is generating a lot of errors in my debug file.

This is part of my debug file:

[03-Oct-2016 07:51:27 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18[03-Oct-2016 09:34:54 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 09:35:05 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 09:42:58 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 09:43:39 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 09:49:03 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 09:52:03 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:00:03 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:01:04 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:08:56 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:09:18 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:10:07 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:10:33 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:52:14 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:52:37 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:54:31 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 10:56:09 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 12:21:23 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 12:22:35 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 12:23:37 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 12:24:50 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 13:43:46 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 15:38:28 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 16:47:16 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 18:07:59 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 19:50:48 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 21:48:40 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 22:53:41 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 23:53:23 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18
[03-Oct-2016 23:56:22 UTC] PHP Notice: Undefined index: SERVER_NAME in /home/content/a2pnexwpnas01_data02/95/3559195/html/wp-content/plugins/count-per-day/counter.php on line 18

Any idea why this should occur?