Fatal error: Uncaught TypeError: Return value of NF_Admin_Metaboxes_Calculations::registerReactMetabox() must be an instance of void, none returned in /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/includes/Admin/Metaboxes/Calculations.php:37 Stack trace: #0 /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/includes/Admin/Metaboxes/Calculations.php(7): NF_Admin_Metaboxes_Calculations->registerReactMetabox() #1 /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/ninja-forms.php(370): NF_Admin_Metaboxes_Calculations->__construct() #2 /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/ninja-forms.php(1223): Ninja_Forms::instance() #3 /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/ninja-forms.php(1226): Ninja_Forms() #4 /home/uniekeconcepten/public_html/wp-settings.php(388): include_once('/home/uniekecon...') #5 /home/uniekeconcepten/public_html/wp-config.php(89): require_once('/home/uniekecon...') #6 /home/uniekeconcepten/public_html/wp-load.php(37 in /home/uniekeconcepten/public_html/wp-content/plugins/ninja-forms/includes/Admin/Metaboxes/Calculations.php on line 37