Display numeric and boolean values in export / listing

Fixes bug that prevents numeric and boolean properties to be displayed in export and backend listings.

Classes/Service/DatabaseStorageService.php

@@ -293,6 +293,12 @@ protected function getStringValue($value, int $indent = 0): string
         if (is_string($value)) {
             return $value;
         }
+        if (is_numeric($value)) {
+            return (string) $value;
+        }
+        if (is_bool($value)) {
+            return ($value ? 'true' : 'false');
+        }
         if (is_object($value) && method_exists($value, '__toString')) {
             return (string)$value;
         }