Merge pull request #687 from Hologos/hotfix/empty-tree-searches

Fixes empty tree searches.

src/Git/Repository.php

@@ -271,6 +271,10 @@ class Repository extends BaseRepository
 
     public function searchTree($query, $branch)
     {
+        if(empty($query)) {
+            return null;
+        }
+
         $query = escapeshellarg($query);
 
         try {