Fall back to boolean on canSelectAcrossSites instead of null (#332)

Author: dnwjn

src/Structures/Nav.php

@@ -18,7 +18,7 @@ public static function fromModel(Model $model)
             ->collections($model->settings['collections'] ?? null)
             ->maxDepth($model->settings['max_depth'] ?? null)
             ->expectsRoot($model->settings['expects_root'] ?? false)
-            ->canSelectAcrossSites($model->settings['select_across_sites'] ?? null)
+            ->canSelectAcrossSites($model->settings['select_across_sites'] ?? false)
             ->model($model);
     }