Merge pull request #118 from ItinerisLtd/postgrid-posttypes-check

fix(PostGrid): `Argument #3 must be of type string

src/Settings/PostGrid.php

@@ -193,6 +193,7 @@ public static function filterBar($settings): string
         if ('main_query' === $settings->data_source) {
             $postTypes = [get_post_type()];
         }
+        $postTypes = array_filter($postTypes);
         if (empty($postTypes)) {
             $postTypes = ['post'];
         }