WordPress detects fatal error in plugin

Since some time WordPress sends a mail when there’s an error in one of the files. As one of my sites uses the shiftcontroller plugin and I’ve got this message now a number of time I thought it a good idea to inform you too. The mail itself is in dutch and as it only explains it’s purpose, I’ve only copied the details section. As the errors are in English I hope this will give you a clue about what’s going on.

As said, I’ve gotten this mail a number of times. The user doesn’t really notice anything.

Foutdetails
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Een fout van het type E_ERROR werd veroorzaakt op regelnummer 75 van het bestand /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/sh4/shifts/view/zoom.php. Foutmelding: Uncaught TypeError: Argument 1 passed to SH4_Shifts_View_Zoom::rows() must be an instance of SH4_Shifts_Model, null given, called in /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/hc3/hookswrapper.php on line 40 and defined in /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/sh4/shifts/view/zoom.php:75
Stack trace:
#0 /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/hc3/hookswrapper.php(40): SH4_Shifts_View_Zoom->rows(NULL)
#1 /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/sh4/shifts/view/zoom.php(40): HC3_HooksWrapper->__call(‘rows’, Array)
#2 /var/www/vhosts/friesebewakingsdienst.nl/medewerkers.friesebewakingsdienst.nl/wp-content/plugins/shiftcontroller/hc3/hookswrapper.php(40): SH4_Shifts_View_Zoom->render(‘715’)
#3 /var/www/vhosts/friesebewakingsdien