Improved CSV-Export of non-string values.

app/Http/Controllers/ResultController.php

@@ -130,10 +130,11 @@ class ResultController extends Controller
                 ->map(function($row) use ($header, $id_header, $id_format, $id) {
                     foreach ($header as $key) {
                         // Fill empty columns with N/A
-                        $row[$key] = $row[$key] ?? config('experiment.n-a-text');
-
-                        // Replace arrays with json
-                        if (is_array($row[$key]))
+                        if ($row[$key] === null)
+                            $row[$key] = config('experiment.n-a-text');
+                        else if (is_string($row[$key]))
+                            ; // pass
+                        else
                             $row[$key] = json_encode($row[$key]);
                     }