Warning in Punch Log page

Repeatable: always
Steps to repeat:
1. Download and install Punchclock
2. Visit Punch Log

Expected result:
Complete punch log without warning messages

Actual result:
Complete punch log with the following warning messages:

Warning: mb_strlen() expects parameter 1 to be string, array given in drupal_strlen() (line 441 of /Applications/XAMPP/xamppfiles/htdocs/entradas/includes/unicode.inc).
Warning: mb_strlen() expects parameter 1 to be string, array given in drupal_strlen() (line 441 of /Applications/XAMPP/xamppfiles/htdocs/entradas/includes/unicode.inc).

Note: when the search boxes are filled and "apply" is pressed, the warning messages disappear. As soon as the user navigates to other page and then, comes back to Punch Log, the error appears again.
It happens with or without the correct permissions enabled and for both the Supervisor and Employee roles.