Fix various phpstan issues.

app/Support/Request/ConvertsDataTypes.php

@@ -102,6 +102,9 @@ trait ConvertsDataTypes
     {
         // assume this all works, because the validator would have caught any errors.
         $parameter      = (string)request()->query->get($field);
+        if('' === $parameter) {
+            return [];
+        }
         $parts          = explode(',', $parameter);
         $sortParameters = [];
         foreach ($parts as $part) {