diff --git a/src/applications/auth/engine/PhabricatorAuthInviteEngine.php b/src/applications/auth/engine/PhabricatorAuthInviteEngine.php
--- a/src/applications/auth/engine/PhabricatorAuthInviteEngine.php
+++ b/src/applications/auth/engine/PhabricatorAuthInviteEngine.php
@@ -125,7 +125,7 @@
   private function handleLoggedInInvite(
     PhabricatorAuthInvite $invite,
     PhabricatorUser $viewer,
-    PhabricatorUserEmail $email = null) {
+    ?PhabricatorUserEmail $email = null) {
 
     if ($email && ($email->getUserPHID() !== $viewer->getPHID())) {
       $other_user = $this->loadUserForEmail($email);
diff --git a/src/applications/base/controller/PhabricatorController.php b/src/applications/base/controller/PhabricatorController.php
--- a/src/applications/base/controller/PhabricatorController.php
+++ b/src/applications/base/controller/PhabricatorController.php
@@ -485,8 +485,8 @@
 
   protected function buildTransactionTimeline(
     PhabricatorApplicationTransactionInterface $object,
-    PhabricatorApplicationTransactionQuery $query = null,
-    PhabricatorMarkupEngine $engine = null,
+    ?PhabricatorApplicationTransactionQuery $query = null,
+    ?PhabricatorMarkupEngine $engine = null,
     $view_data = array()) {
 
     $request = $this->getRequest();
diff --git a/src/applications/calendar/import/PhabricatorCalendarImportEngine.php b/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
--- a/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
+++ b/src/applications/calendar/import/PhabricatorCalendarImportEngine.php
@@ -55,7 +55,7 @@
   final protected function importEventDocument(
     PhabricatorUser $viewer,
     PhabricatorCalendarImport $import,
-    PhutilCalendarRootNode $root = null) {
+    ?PhutilCalendarRootNode $root = null) {
 
     $event_type = PhutilCalendarEventNode::NODETYPE;
 
diff --git a/src/applications/calendar/parser/data/PhutilCalendarRecurrenceSet.php b/src/applications/calendar/parser/data/PhutilCalendarRecurrenceSet.php
--- a/src/applications/calendar/parser/data/PhutilCalendarRecurrenceSet.php
+++ b/src/applications/calendar/parser/data/PhutilCalendarRecurrenceSet.php
@@ -21,8 +21,8 @@
   }
 
   public function getEventsBetween(
-    PhutilCalendarDateTime $start = null,
-    PhutilCalendarDateTime $end = null,
+    ?PhutilCalendarDateTime $start = null,
+    ?PhutilCalendarDateTime $end = null,
     $limit = null) {
 
     if ($end === null && $limit === null) {
diff --git a/src/applications/conduit/controller/PhabricatorConduitAPIController.php b/src/applications/conduit/controller/PhabricatorConduitAPIController.php
--- a/src/applications/conduit/controller/PhabricatorConduitAPIController.php
+++ b/src/applications/conduit/controller/PhabricatorConduitAPIController.php
@@ -527,9 +527,9 @@
 
   private function buildHumanReadableResponse(
     $method,
-    ConduitAPIRequest $request = null,
+    ?ConduitAPIRequest $request = null,
     $result = null,
-    ConduitAPIMethod $method_implementation = null) {
+    ?ConduitAPIMethod $method_implementation = null) {
 
     $param_rows = array();
     $param_rows[] = array('Method', $this->renderAPIValue($method));
diff --git a/src/applications/conduit/method/ConduitGetCertificateConduitAPIMethod.php b/src/applications/conduit/method/ConduitGetCertificateConduitAPIMethod.php
--- a/src/applications/conduit/method/ConduitGetCertificateConduitAPIMethod.php
+++ b/src/applications/conduit/method/ConduitGetCertificateConduitAPIMethod.php
@@ -80,7 +80,7 @@
 
   private function logFailure(
     ConduitAPIRequest $request,
-    PhabricatorConduitCertificateToken $info = null) {
+    ?PhabricatorConduitCertificateToken $info = null) {
 
     $log = PhabricatorUserLog::initializeNewLog(
         $request->getUser(),
diff --git a/src/applications/config/controller/settings/PhabricatorConfigSettingsListController.php b/src/applications/config/controller/settings/PhabricatorConfigSettingsListController.php
--- a/src/applications/config/controller/settings/PhabricatorConfigSettingsListController.php
+++ b/src/applications/config/controller/settings/PhabricatorConfigSettingsListController.php
@@ -75,7 +75,7 @@
 
   private function newConfigOptionView(
     PhabricatorConfigOption $option,
-    PhabricatorConfigEntry $stored_value = null) {
+    ?PhabricatorConfigEntry $stored_value = null) {
 
     $summary = $option->getSummary();
 
diff --git a/src/applications/conpherence/view/ConpherenceDurableColumnView.php b/src/applications/conpherence/view/ConpherenceDurableColumnView.php
--- a/src/applications/conpherence/view/ConpherenceDurableColumnView.php
+++ b/src/applications/conpherence/view/ConpherenceDurableColumnView.php
@@ -32,7 +32,7 @@
   }
 
   public function setSelectedConpherence(
-    ConpherenceThread $conpherence = null) {
+    ?ConpherenceThread $conpherence = null) {
     $this->selectedConpherence = $conpherence;
     return $this;
   }
diff --git a/src/applications/dashboard/controller/dashboard/PhabricatorDashboardAdjustController.php b/src/applications/dashboard/controller/dashboard/PhabricatorDashboardAdjustController.php
--- a/src/applications/dashboard/controller/dashboard/PhabricatorDashboardAdjustController.php
+++ b/src/applications/dashboard/controller/dashboard/PhabricatorDashboardAdjustController.php
@@ -204,7 +204,7 @@
   private function handleMoveRequest(
     PhabricatorDashboard $dashboard,
     PhabricatorDashboardPanelRef $panel_ref,
-    PhabricatorDashboardPanelRef $after_ref = null) {
+    ?PhabricatorDashboardPanelRef $after_ref = null) {
 
     $request = $this->getRequest();
     $request->validateCSRF();
diff --git a/src/applications/dashboard/layoutconfig/PhabricatorDashboardPanelRefList.php b/src/applications/dashboard/layoutconfig/PhabricatorDashboardPanelRefList.php
--- a/src/applications/dashboard/layoutconfig/PhabricatorDashboardPanelRefList.php
+++ b/src/applications/dashboard/layoutconfig/PhabricatorDashboardPanelRefList.php
@@ -121,7 +121,7 @@
   public function movePanelRef(
     PhabricatorDashboardPanelRef $target,
     $column_key,
-    PhabricatorDashboardPanelRef $after = null) {
+    ?PhabricatorDashboardPanelRef $after = null) {
 
     $target->setColumnKey($column_key);
 
diff --git a/src/applications/differential/conduit/DifferentialConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialConduitAPIMethod.php
@@ -20,7 +20,7 @@
 
   protected function buildInlineInfoDictionary(
     DifferentialInlineComment $inline,
-    DifferentialChangeset $changeset = null) {
+    ?DifferentialChangeset $changeset = null) {
 
     $file_path = null;
     $diff_id = null;
diff --git a/src/applications/differential/controller/DifferentialRevisionViewController.php b/src/applications/differential/controller/DifferentialRevisionViewController.php
--- a/src/applications/differential/controller/DifferentialRevisionViewController.php
+++ b/src/applications/differential/controller/DifferentialRevisionViewController.php
@@ -863,8 +863,8 @@
 
   private function loadChangesetsAndVsMap(
     DifferentialDiff $target,
-    DifferentialDiff $diff_vs = null,
-    PhabricatorRepository $repository = null) {
+    ?DifferentialDiff $diff_vs = null,
+    ?PhabricatorRepository $repository = null) {
     $viewer = $this->getViewer();
 
     $load_diffs = array($target);
@@ -1049,7 +1049,7 @@
     array $changesets,
     array $vs_changesets,
     array $vs_map,
-    PhabricatorRepository $repository = null) {
+    ?PhabricatorRepository $repository = null) {
 
     assert_instances_of($changesets,    'DifferentialChangeset');
     assert_instances_of($vs_changesets, 'DifferentialChangeset');
diff --git a/src/applications/differential/render/DifferentialChangesetRenderer.php b/src/applications/differential/render/DifferentialChangesetRenderer.php
--- a/src/applications/differential/render/DifferentialChangesetRenderer.php
+++ b/src/applications/differential/render/DifferentialChangesetRenderer.php
@@ -105,7 +105,7 @@
     return $this->depthOnlyLines;
   }
 
-  public function attachOldFile(PhabricatorFile $old = null) {
+  public function attachOldFile(?PhabricatorFile $old = null) {
     $this->oldFile = $old;
     return $this;
   }
@@ -121,7 +121,7 @@
     return (bool)$this->oldFile;
   }
 
-  public function attachNewFile(PhabricatorFile $new = null) {
+  public function attachNewFile(?PhabricatorFile $new = null) {
     $this->newFile = $new;
     return $this;
   }
diff --git a/src/applications/diffusion/controller/DiffusionLastModifiedController.php b/src/applications/diffusion/controller/DiffusionLastModifiedController.php
--- a/src/applications/diffusion/controller/DiffusionLastModifiedController.php
+++ b/src/applications/diffusion/controller/DiffusionLastModifiedController.php
@@ -84,7 +84,7 @@
 
   private function renderColumns(
     DiffusionRequest $drequest,
-    PhabricatorRepositoryCommit $commit = null,
+    ?PhabricatorRepositoryCommit $commit = null,
     $lint = null) {
     $viewer = $this->getViewer();
 
diff --git a/src/applications/diffusion/data/DiffusionLocalRepositoryFilter.php b/src/applications/diffusion/data/DiffusionLocalRepositoryFilter.php
--- a/src/applications/diffusion/data/DiffusionLocalRepositoryFilter.php
+++ b/src/applications/diffusion/data/DiffusionLocalRepositoryFilter.php
@@ -20,7 +20,7 @@
     return $this->viewer;
   }
 
-  public function setDevice(AlmanacDevice $device = null) {
+  public function setDevice(?AlmanacDevice $device = null) {
     $this->device = $device;
     return $this;
   }
diff --git a/src/applications/diffusion/document/DiffusionDocumentRenderingEngine.php b/src/applications/diffusion/document/DiffusionDocumentRenderingEngine.php
--- a/src/applications/diffusion/document/DiffusionDocumentRenderingEngine.php
+++ b/src/applications/diffusion/document/DiffusionDocumentRenderingEngine.php
@@ -65,7 +65,7 @@
 
   protected function addApplicationCrumbs(
     PHUICrumbsView $crumbs,
-    PhabricatorDocumentRef $ref = null) {
+    ?PhabricatorDocumentRef $ref = null) {
     return;
   }
 
diff --git a/src/applications/diffusion/query/DiffusionCommitRevisionQuery.php b/src/applications/diffusion/query/DiffusionCommitRevisionQuery.php
--- a/src/applications/diffusion/query/DiffusionCommitRevisionQuery.php
+++ b/src/applications/diffusion/query/DiffusionCommitRevisionQuery.php
@@ -68,7 +68,7 @@
     PhabricatorUser $viewer,
     $source_object,
     array $object_names,
-    PhabricatorRepository $repository_scope = null) {
+    ?PhabricatorRepository $repository_scope = null) {
 
     // Fetch commits first, since we need to load data on commits in order
     // to identify associated revisions later on.
diff --git a/src/applications/files/diff/PhabricatorDocumentEngineBlocks.php b/src/applications/files/diff/PhabricatorDocumentEngineBlocks.php
--- a/src/applications/files/diff/PhabricatorDocumentEngineBlocks.php
+++ b/src/applications/files/diff/PhabricatorDocumentEngineBlocks.php
@@ -39,7 +39,7 @@
   }
 
   public function addBlockList(
-    PhabricatorDocumentRef $ref = null,
+    ?PhabricatorDocumentRef $ref = null,
     array $blocks = array()) {
 
     assert_instances_of($blocks, 'PhabricatorDocumentEngineBlock');
diff --git a/src/applications/files/document/PhabricatorDocumentEngine.php b/src/applications/files/document/PhabricatorDocumentEngine.php
--- a/src/applications/files/document/PhabricatorDocumentEngine.php
+++ b/src/applications/files/document/PhabricatorDocumentEngine.php
@@ -32,8 +32,8 @@
   }
 
   public function canDiffDocuments(
-    PhabricatorDocumentRef $uref = null,
-    PhabricatorDocumentRef $vref = null) {
+    ?PhabricatorDocumentRef $uref = null,
+    ?PhabricatorDocumentRef $vref = null) {
     return false;
   }
 
diff --git a/src/applications/files/document/PhabricatorImageDocumentEngine.php b/src/applications/files/document/PhabricatorImageDocumentEngine.php
--- a/src/applications/files/document/PhabricatorImageDocumentEngine.php
+++ b/src/applications/files/document/PhabricatorImageDocumentEngine.php
@@ -18,8 +18,8 @@
   }
 
   public function canDiffDocuments(
-    PhabricatorDocumentRef $uref = null,
-    PhabricatorDocumentRef $vref = null) {
+    ?PhabricatorDocumentRef $uref = null,
+    ?PhabricatorDocumentRef $vref = null) {
 
     // For now, we can only render a rich image diff if the documents have
     // their data stored in Files already.
@@ -36,8 +36,8 @@
   }
 
   public function newEngineBlocks(
-    PhabricatorDocumentRef $uref = null,
-    PhabricatorDocumentRef $vref = null) {
+    ?PhabricatorDocumentRef $uref = null,
+    ?PhabricatorDocumentRef $vref = null) {
 
     if ($uref) {
       $u_blocks = $this->newDiffBlocks($uref);
diff --git a/src/applications/files/document/PhabricatorJupyterDocumentEngine.php b/src/applications/files/document/PhabricatorJupyterDocumentEngine.php
--- a/src/applications/files/document/PhabricatorJupyterDocumentEngine.php
+++ b/src/applications/files/document/PhabricatorJupyterDocumentEngine.php
@@ -36,14 +36,14 @@
   }
 
   public function canDiffDocuments(
-    PhabricatorDocumentRef $uref = null,
-    PhabricatorDocumentRef $vref = null) {
+    ?PhabricatorDocumentRef $uref = null,
+    ?PhabricatorDocumentRef $vref = null) {
     return true;
   }
 
   public function newEngineBlocks(
-    PhabricatorDocumentRef $uref = null,
-    PhabricatorDocumentRef $vref = null) {
+    ?PhabricatorDocumentRef $uref = null,
+    ?PhabricatorDocumentRef $vref = null) {
 
     $blocks = new PhabricatorDocumentEngineBlocks();
 
diff --git a/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php b/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
--- a/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
+++ b/src/applications/files/document/render/PhabricatorDocumentRenderingEngine.php
@@ -329,7 +329,7 @@
 
   protected function addApplicationCrumbs(
     PHUICrumbsView $crumbs,
-    PhabricatorDocumentRef $ref = null) {
+    ?PhabricatorDocumentRef $ref = null) {
     return;
   }
 
diff --git a/src/applications/files/document/render/PhabricatorFileDocumentRenderingEngine.php b/src/applications/files/document/render/PhabricatorFileDocumentRenderingEngine.php
--- a/src/applications/files/document/render/PhabricatorFileDocumentRenderingEngine.php
+++ b/src/applications/files/document/render/PhabricatorFileDocumentRenderingEngine.php
@@ -35,7 +35,7 @@
 
   protected function addApplicationCrumbs(
     PHUICrumbsView $crumbs,
-    PhabricatorDocumentRef $ref = null) {
+    ?PhabricatorDocumentRef $ref = null) {
 
     if ($ref) {
       $file = $ref->getFile();
diff --git a/src/applications/project/__tests__/PhabricatorProjectCoreTestCase.php b/src/applications/project/__tests__/PhabricatorProjectCoreTestCase.php
--- a/src/applications/project/__tests__/PhabricatorProjectCoreTestCase.php
+++ b/src/applications/project/__tests__/PhabricatorProjectCoreTestCase.php
@@ -1534,7 +1534,7 @@
 
   private function createProject(
     PhabricatorUser $user,
-    PhabricatorProject $parent = null,
+    ?PhabricatorProject $parent = null,
     $is_milestone = false) {
 
     $project = PhabricatorProject::initializeNewProject($user, $parent);
diff --git a/src/applications/project/view/ProjectBoardTaskCard.php b/src/applications/project/view/ProjectBoardTaskCard.php
--- a/src/applications/project/view/ProjectBoardTaskCard.php
+++ b/src/applications/project/view/ProjectBoardTaskCard.php
@@ -54,7 +54,7 @@
     return $this->task;
   }
 
-  public function setOwner(PhabricatorObjectHandle $owner = null) {
+  public function setOwner(?PhabricatorObjectHandle $owner = null) {
     $this->owner = $owner;
     return $this;
   }
diff --git a/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php b/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
--- a/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
+++ b/src/applications/repository/daemon/PhabricatorRepositoryPullLocalDaemon.php
@@ -405,7 +405,7 @@
   private function loadPullableRepositories(
     array $include,
     array $exclude,
-    AlmanacDevice $device = null) {
+    ?AlmanacDevice $device = null) {
 
     $query = id(new PhabricatorRepositoryQuery())
       ->setViewer($this->getViewer());
diff --git a/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php b/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
--- a/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
+++ b/src/applications/repository/engine/PhabricatorRepositoryPullEngine.php
@@ -172,7 +172,7 @@
     $this->donePull();
   }
 
-  private function abortPull($message, Exception $ex = null) {
+  private function abortPull($message, ?Exception $ex = null) {
     $code_error = PhabricatorRepositoryStatusMessage::CODE_ERROR;
     $this->updateRepositoryInitStatus($code_error, $message);
     if ($ex) {
diff --git a/src/applications/search/compiler/PhutilSearchQueryCompiler.php b/src/applications/search/compiler/PhutilSearchQueryCompiler.php
--- a/src/applications/search/compiler/PhutilSearchQueryCompiler.php
+++ b/src/applications/search/compiler/PhutilSearchQueryCompiler.php
@@ -437,7 +437,7 @@
 
   private function renderToken(
     PhutilSearchQueryToken $token,
-    PhutilSearchStemmer $stemmer = null) {
+    ?PhutilSearchStemmer $stemmer = null) {
     $value = $token->getValue();
 
     if ($stemmer) {
diff --git a/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php b/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
--- a/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
+++ b/src/applications/search/compiler/__tests__/PhutilSearchQueryCompilerTestCase.php
@@ -227,7 +227,7 @@
   private function assertCompileQueries(
     array $tests,
     $operators = null,
-    PhutilSearchStemmer $stemmer = null) {
+    ?PhutilSearchStemmer $stemmer = null) {
     foreach ($tests as $input => $expect) {
       $caught = null;
 
diff --git a/src/applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php b/src/applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php
--- a/src/applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php
+++ b/src/applications/search/fulltextstorage/PhabricatorElasticFulltextStorageEngine.php
@@ -263,7 +263,7 @@
       $exceptions);
   }
 
-  public function indexExists(PhabricatorElasticsearchHost $host = null) {
+  public function indexExists(?PhabricatorElasticsearchHost $host = null) {
     if (!$host) {
       $host = $this->getHostForRead();
     }
@@ -397,7 +397,7 @@
     return $data;
   }
 
-  public function indexIsSane(PhabricatorElasticsearchHost $host = null) {
+  public function indexIsSane(?PhabricatorElasticsearchHost $host = null) {
     if (!$host) {
       $host = $this->getHostForRead();
     }
@@ -476,7 +476,7 @@
     $this->executeRequest($host, '/', $data, 'PUT');
   }
 
-  public function getIndexStats(PhabricatorElasticsearchHost $host = null) {
+  public function getIndexStats(?PhabricatorElasticsearchHost $host = null) {
     if ($this->version < 2) {
       return false;
     }
diff --git a/src/applications/search/menuitem/PhabricatorDashboardProfileMenuItem.php b/src/applications/search/menuitem/PhabricatorDashboardProfileMenuItem.php
--- a/src/applications/search/menuitem/PhabricatorDashboardProfileMenuItem.php
+++ b/src/applications/search/menuitem/PhabricatorDashboardProfileMenuItem.php
@@ -27,7 +27,7 @@
     return true;
   }
 
-  private function attachDashboard(PhabricatorDashboard $dashboard = null) {
+  private function attachDashboard(?PhabricatorDashboard $dashboard = null) {
     $this->dashboard = $dashboard;
     return $this;
   }
diff --git a/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php b/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
--- a/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
+++ b/src/applications/search/query/PhabricatorSearchApplicationSearchEngine.php
@@ -201,7 +201,7 @@
   }
 
   public static function getIndexableDocumentTypes(
-    PhabricatorUser $viewer = null) {
+    ?PhabricatorUser $viewer = null) {
 
     // TODO: This is inelegant and not very efficient, but gets us reasonable
     // results. It would be nice to do this more elegantly.
diff --git a/src/applications/settings/panel/PhabricatorEmailPreferencesSettingsPanel.php b/src/applications/settings/panel/PhabricatorEmailPreferencesSettingsPanel.php
--- a/src/applications/settings/panel/PhabricatorEmailPreferencesSettingsPanel.php
+++ b/src/applications/settings/panel/PhabricatorEmailPreferencesSettingsPanel.php
@@ -146,7 +146,7 @@
     return $form_box;
   }
 
-  private function getAllEditorsWithTags(PhabricatorUser $user = null) {
+  private function getAllEditorsWithTags(?PhabricatorUser $user = null) {
     $editors = id(new PhutilClassMapQuery())
       ->setAncestorClass('PhabricatorApplicationTransactionEditor')
       ->setFilterMethod('getMailTagsMap')
@@ -165,7 +165,7 @@
     return $editors;
   }
 
-  private function getAllTags(PhabricatorUser $user = null) {
+  private function getAllTags(?PhabricatorUser $user = null) {
     $tags = array();
     foreach ($this->getAllEditorsWithTags($user) as $editor) {
       $tags += $editor->getMailTagsMap();
diff --git a/src/applications/settings/setting/PhabricatorSetting.php b/src/applications/settings/setting/PhabricatorSetting.php
--- a/src/applications/settings/setting/PhabricatorSetting.php
+++ b/src/applications/settings/setting/PhabricatorSetting.php
@@ -4,7 +4,7 @@
 
   private $viewer = false;
 
-  public function setViewer(PhabricatorUser $viewer = null) {
+  public function setViewer(?PhabricatorUser $viewer = null) {
     $this->viewer = $viewer;
     return $this;
   }
diff --git a/src/applications/transactions/draft/PhabricatorDraftEngine.php b/src/applications/transactions/draft/PhabricatorDraftEngine.php
--- a/src/applications/transactions/draft/PhabricatorDraftEngine.php
+++ b/src/applications/transactions/draft/PhabricatorDraftEngine.php
@@ -27,7 +27,7 @@
   }
 
   final public function setVersionedDraft(
-    PhabricatorVersionedDraft $draft = null) {
+    ?PhabricatorVersionedDraft $draft = null) {
     $this->hasVersionedDraft = true;
     $this->versionedDraft = $draft;
     return $this;
diff --git a/src/infrastructure/diff/interface/PhabricatorInlineComment.php b/src/infrastructure/diff/interface/PhabricatorInlineComment.php
--- a/src/infrastructure/diff/interface/PhabricatorInlineComment.php
+++ b/src/infrastructure/diff/interface/PhabricatorInlineComment.php
@@ -288,7 +288,7 @@
 
   public function attachVersionedDraftForViewer(
     PhabricatorUser $viewer,
-    PhabricatorVersionedDraft $draft = null) {
+    ?PhabricatorVersionedDraft $draft = null) {
 
     $key = $viewer->getCacheFragment();
     $this->versionedDrafts[$key] = $draft;
@@ -415,7 +415,7 @@
 
   private function getWireContentStateMap(
     $is_edit,
-    PhabricatorUser $viewer = null) {
+    ?PhabricatorUser $viewer = null) {
 
     $initial_state = $this->getInitialContentState();
     $committed_state = $this->getCommittedContentState();
diff --git a/src/infrastructure/util/__tests__/PhabricatorGlobalLockTestCase.php b/src/infrastructure/util/__tests__/PhabricatorGlobalLockTestCase.php
--- a/src/infrastructure/util/__tests__/PhabricatorGlobalLockTestCase.php
+++ b/src/infrastructure/util/__tests__/PhabricatorGlobalLockTestCase.php
@@ -205,7 +205,7 @@
 
   private function tryHeldLock(
     $lock_name,
-    AphrontDatabaseConnection $conn = null) {
+    ?AphrontDatabaseConnection $conn = null) {
 
     $lock = PhabricatorGlobalLock::newLock($lock_name);
 
diff --git a/src/view/AphrontDialogView.php b/src/view/AphrontDialogView.php
--- a/src/view/AphrontDialogView.php
+++ b/src/view/AphrontDialogView.php
@@ -273,7 +273,7 @@
   }
 
   public function setValidationException(
-    PhabricatorApplicationTransactionValidationException $ex = null) {
+    ?PhabricatorApplicationTransactionValidationException $ex = null) {
     $this->validationException = $ex;
     return $this;
   }
diff --git a/src/view/phui/PHUIObjectBoxView.php b/src/view/phui/PHUIObjectBoxView.php
--- a/src/view/phui/PHUIObjectBoxView.php
+++ b/src/view/phui/PHUIObjectBoxView.php
@@ -135,7 +135,7 @@
   }
 
   public function setValidationException(
-    PhabricatorApplicationTransactionValidationException $ex = null) {
+    ?PhabricatorApplicationTransactionValidationException $ex = null) {
     $this->validationException = $ex;
     return $this;
   }