DEBUG.LOG – PHP Notice: Undefined index: HTTP_HOST

Hello dear Support-Team.

We are using the Free-Plugin of iThemes Security and getting following DEBUG Info.

[08-Mar-2017 15:11:35 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[08-Mar-2017 16:40:57 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[08-Mar-2017 18:47:42 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[08-Mar-2017 20:09:31 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[08-Mar-2017 20:24:46 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[08-Mar-2017 20:29:03 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 00:49:21 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 02:30:50 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 02:46:16 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 04:14:23 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 04:26:30 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 04:28:11 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 05:36:54 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 06:19:19 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126
[09-Mar-2017 08:01:46 UTC] PHP Notice:  Undefined index: HTTP_HOST in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/better-wp-security/core/modules/ssl/class-itsec-ssl.php on line 126

Which information i can give you, to resolve the problem?

Thank you very much.