Removing logic to set fields to 'null'.

src/SolrEngine.php

@@ -19,16 +19,6 @@ class SolrEngine extends Engine
         $update = \Solr::createUpdate();
         $models->each(function ($model) use (&$update) {
             $searchableArray = $model->toSearchableArray();
-            foreach ($searchableArray as $key => $value) {
-                if (empty($value) && !is_numeric($value)) {
-                    if (is_array($value)) {
-                        $value = ['null'];
-                    } else {
-                        $value = 'null';
-                    }
-                    $searchableArray[$key] = $value;
-                }
-            }
             $document = $update->createDocument($searchableArray);
             $update->addDocument($document);
         });