Don't pass null as second parameter to preg_match (#190)

Author: phpfui

src/Gitonomy/Git/Parser/DiffParser.php

@@ -90,6 +90,8 @@ protected function doParse()
 
             $oldName = $oldName === '/dev/null' ? null : substr($oldName, 2);
             $newName = $newName === '/dev/null' ? null : substr($newName, 2);
+            $oldIndex !== null ?: '';
+            $newIndex !== null ?: '';
             $oldIndex = preg_match('/^0+$/', $oldIndex) ? null : $oldIndex;
             $newIndex = preg_match('/^0+$/', $newIndex) ? null : $newIndex;
             $file = new File($oldName, $newName, $oldMode, $newMode, $oldIndex, $newIndex, $isBinary);