Warning: Missing argument 2 for GD_System_Plugin_Metrics:: a

Im getting this error after a new user tries to register:

‘ Warning: Missing argument 2 for GD_System_Plugin_Metrics::{closure}() in /home/content/a2pnexwpnas04_data01/54/3377754/html/wp-content/mu-plugins/gd-system-plugin/class-gd-system-plugin-metrics.php on line 29

Warning: Cannot modify header information – headers already sent by (output started at /home/content/a2pnexwpnas04_data01/54/3377754/html/wp-content/mu-plugins/gd-system-plugin/class-gd-system-plugin-metrics.php:29) in /home/content/a2pnexwpnas04_data01/54/3377754/html/wp-includes/pluggable.php on line 1167 ‘

I have no idea what is causing it and cant figure out how to fix it.please somebody help!