Code results in "array_merge() does not accept unknown named parameters"

Problem/Motivation

The code

      if (count($relatable_resource_types) > 0) {
        $message .= sprintf(' Possible values: %s', implode(', ', array_unique(array_merge(...$relatable_resource_types))));
      }

Results in errors because array merge does not take named parameters and $relatable_resource_types has keys.

Steps to reproduce

Try and use a missing relationship - you'll get an unhelpful error about array_merge

Proposed resolution

Change the code to:

      if (count($relatable_resource_types) > 0) {
        $message .= sprintf(' Possible values: %s', implode(', ', array_unique(array_merge(...array_values($relatable_resource_types)))));
      }

Remaining tasks

User interface changes

API changes

Data model changes