diff --git a/src/applications/diffusion/controller/DiffusionHistoryController.php b/src/applications/diffusion/controller/DiffusionHistoryController.php
--- a/src/applications/diffusion/controller/DiffusionHistoryController.php
+++ b/src/applications/diffusion/controller/DiffusionHistoryController.php
@@ -50,7 +50,7 @@
     // ancestors appropriately, but this would currrently be prohibitively
     // expensive in the general case.
 
-    $show_graph = !strlen($drequest->getPath());
+    $show_graph = !phutil_nonempty_string($drequest->getPath());
     if ($show_graph) {
       $history_list
         ->setParents($history_results['parents'])
@@ -98,11 +98,10 @@
     $viewer = $this->getViewer();
     $repository = $drequest->getRepository();
 
-    $no_path = !strlen($drequest->getPath());
-    if ($no_path) {
-      $header_text = pht('History');
-    } else {
+    if (phutil_nonempty_string($drequest->getPath())) {
       $header_text = $this->renderPathLinks($drequest, $mode = 'history');
+    } else {
+      $header_text = pht('History');
     }
 
     $header = id(new PHUIHeaderView())
diff --git a/src/applications/diffusion/query/pathid/DiffusionPathIDQuery.php b/src/applications/diffusion/query/pathid/DiffusionPathIDQuery.php
--- a/src/applications/diffusion/query/pathid/DiffusionPathIDQuery.php
+++ b/src/applications/diffusion/query/pathid/DiffusionPathIDQuery.php
@@ -48,6 +48,9 @@
    */
   public static function normalizePath($path) {
 
+    // Ensure we have a string, not a null.
+    $path = coalesce($path, '');
+
     // Normalize to single slashes, e.g. "///" => "/".
     $path = preg_replace('@[/]{2,}@', '/', $path);