diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -487,6 +487,7 @@
     'DifferentialChangesetRenderer' => 'applications/differential/render/DifferentialChangesetRenderer.php',
     'DifferentialChangesetSearchConduitAPIMethod' => 'applications/differential/conduit/DifferentialChangesetSearchConduitAPIMethod.php',
     'DifferentialChangesetSearchEngine' => 'applications/differential/query/DifferentialChangesetSearchEngine.php',
+    'DifferentialChangesetTestCase' => 'applications/differential/storage/__tests__/DifferentialChangesetTestCase.php',
     'DifferentialChangesetTestRenderer' => 'applications/differential/render/DifferentialChangesetTestRenderer.php',
     'DifferentialChangesetTwoUpRenderer' => 'applications/differential/render/DifferentialChangesetTwoUpRenderer.php',
     'DifferentialChangesetTwoUpTestRenderer' => 'applications/differential/render/DifferentialChangesetTwoUpTestRenderer.php',
@@ -6497,6 +6498,7 @@
     'DifferentialChangesetRenderer' => 'Phobject',
     'DifferentialChangesetSearchConduitAPIMethod' => 'PhabricatorSearchEngineAPIMethod',
     'DifferentialChangesetSearchEngine' => 'PhabricatorApplicationSearchEngine',
+    'DifferentialChangesetTestCase' => 'PhabricatorTestCase',
     'DifferentialChangesetTestRenderer' => 'DifferentialChangesetRenderer',
     'DifferentialChangesetTwoUpRenderer' => 'DifferentialChangesetHTMLRenderer',
     'DifferentialChangesetTwoUpTestRenderer' => 'DifferentialChangesetTestRenderer',
diff --git a/src/applications/differential/storage/DifferentialChangeset.php b/src/applications/differential/storage/DifferentialChangeset.php
--- a/src/applications/differential/storage/DifferentialChangeset.php
+++ b/src/applications/differential/storage/DifferentialChangeset.php
@@ -324,11 +324,8 @@
   }
 
   public function getOldStatePathVector() {
-    $path = $this->getOldFile();
-    if (!strlen($path)) {
-      $path = $this->getFilename();
-    }
 
+    $path = $this->getOldFile() || $this->getFilename() || '';
     $path = trim($path, '/');
     $path = explode('/', $path);
 
diff --git a/src/applications/differential/storage/__tests__/DifferentialChangesetTestCase.php b/src/applications/differential/storage/__tests__/DifferentialChangesetTestCase.php
new file mode 100644
--- /dev/null
+++ b/src/applications/differential/storage/__tests__/DifferentialChangesetTestCase.php
@@ -0,0 +1,16 @@
+<?php
+
+final class DifferentialChangesetTestCase extends PhabricatorTestCase {
+
+  public function testPhp81() {
+    $diff_change_set = new DifferentialChangeset();
+    try {
+      $old_state_vector = $diff_change_set->getOldStatePathVector();
+      $this->assertTrue(true, 'getOldStatePathVector did not throw an error');
+    } catch (Throwable $ex) {
+      $this->assertTrue(false,
+        'getOldStatePathVector threw an exception:'.$ex->getMessage());
+    }
+  }
+
+}