array_reduce() expects parameter 2 to be a valid callback

[nilshoerrmann]

Using Members (integration) on Symphony 2.3 throws the following error when creating a new member;

Symphony Warning: array_reduce() expects parameter 2 to be a valid callback, function '__reduceType' not found or invalid function name

An error occurred in /Users/nilshoerrmann/Sites/Webseiten/durchgedreht24.de/symphony/lib/toolkit/events/class.event.section.php around line 115

110
111                 foreach($errors as $field_id => $message){
112                     $field = FieldManager::fetch($field_id);
113
114                     if(is_array($fields[$field->get('element_name')])) {
115                         $type = array_reduce($fields[$field->get('element_name')], '__reduceType');
116                     }
117                     else {
118                         $type = ($fields[$field->get('element_name')] == '') ? 'missing' : 'invalid';
119                     }

[nilshoerrmann]

This seems more to be a core error – moving the topic there, closing this issue.
See #1371.