[Plugin: Asynchronous Google Analytics for WordPress] error notice in main blog

plugin version 1.0.3

when wordpress is in debug mode and accessing the main blog area:

Notice: Undefined index: HTTP_REFERER in wp-content/plugins/async-google-analytics/asyncgoogleanalytics.php on line 371

Call Stack:
    0.0001     316936   1. {main}() index.php:0
    0.0001     317448   2. require('wp-blog-header.php') index.php:17
    0.1326    3285676   3. require_once('wp-includes/template-loader.php') wp-blog-header.php:16
    0.1360    3286800   4. include('wp-content/themes/mflp_custom/page-nocomments.php') wp-includes/template-loader.php:43
    0.1360    3286800   5. get_header() wp-content/themes/mflp_custom/page-nocomments.php:6
    0.1360    3287308   6. locate_template() wp-includes/general-template.php:34
    0.1360    3287512   7. load_template() wp-includes/theme.php:1062
    0.1363    3297980   8. require_once('wp-content/themes/mflp_custom/header.php') wp-includes/theme.php:1086
    0.1422    3308856   9. wp_head() wp-content/themes/mflp_custom/header.php:10
    0.1422    3308932  10. do_action() wp-includes/general-template.php:1566
    0.1593    3319976  11. call_user_func_array() wp-includes/plugin.php:395
    0.1593    3320004  12. AGA_Filter::spool_analytics() wp-includes/plugin.php:0