Fix PHP 8.1 Diffusion history errors

Summary:
Fix multiple PHP 8.1 errors when viewing Diffusion history.

Fixes T15573

Test Plan: View a diffusion history page. Eg https://my.php81.phorge.site/source/myrepo/history/master/

Reviewers: O1 Blessed Committers, speck

Reviewed By: O1 Blessed Committers, speck

Subscribers: speck, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15573

Differential Revision: https://we.phorge.it/D25366

src/applications/diffusion/controller/DiffusionHistoryController.php

@@ -50,7 +50,7 @@ final class DiffusionHistoryController extends DiffusionController {
     // 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 @@ final class DiffusionHistoryController extends DiffusionController {
     $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())

src/applications/diffusion/query/pathid/DiffusionPathIDQuery.php

@@ -48,6 +48,9 @@ final class DiffusionPathIDQuery extends Phobject {
    */
   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);