diff --git a/classes/migration/upgrade/v3_4_0/PreflightCheckMigration.php b/classes/migration/upgrade/v3_4_0/PreflightCheckMigration.php
index 751f048bedc..c9b685cf29d 100644
--- a/classes/migration/upgrade/v3_4_0/PreflightCheckMigration.php
+++ b/classes/migration/upgrade/v3_4_0/PreflightCheckMigration.php
@@ -234,7 +234,7 @@ protected function buildOrphanedEntityProcessor(): void
             $affectedRows = 0;
             $rows = DB::table('publications AS p')
                 ->join('publication_settings AS ps', 'ps.publication_id', '=', 'p.publication_id')
-                ->leftJoin('issues AS i', DB::raw('CAST(i.issue_id AS CHAR(20))'), '=', 'ps.setting_value')
+                ->leftJoin('issues AS i', 'ps.setting_value', '=', DB::raw('CAST(i.issue_id AS CHAR(20))'))
                 ->where('ps.setting_name', 'issueId')
                 ->whereNull('i.issue_id')
                 ->get(['p.submission_id', 'p.publication_id', 'ps.setting_value']);
diff --git a/classes/observers/events/UsageEvent.php b/classes/observers/events/UsageEvent.php
index 29199c8583d..4a3b5f39fce 100644
--- a/classes/observers/events/UsageEvent.php
+++ b/classes/observers/events/UsageEvent.php
@@ -34,11 +34,11 @@ class UsageEvent extends \PKP\observers\events\UsageEvent
     public function __construct(
         int $assocType,
         Context $context,
-        Submission $submission = null,
-        Representation $galley = null,
-        SubmissionFile $submissionFile = null,
-        Issue $issue = null,
-        IssueGalley $issueGalley = null
+        ?Submission $submission = null,
+        ?Representation $galley = null,
+        ?SubmissionFile $submissionFile = null,
+        ?Issue $issue = null,
+        ?IssueGalley $issueGalley = null
     ) {
         $this->issue = $issue;
         $this->issueGalley = $issueGalley;
diff --git a/classes/section/Section.php b/classes/section/Section.php
index d852ccaada3..5db69fe3487 100644
--- a/classes/section/Section.php
+++ b/classes/section/Section.php
@@ -36,7 +36,7 @@ public function getAbbrev(?string $locale): string|array|null
         return $this->getData('abbrev', $locale);
     }
 
-    public function setAbbrev(string|array $abbrev, string $locale = null): void
+    public function setAbbrev(string|array $abbrev, ?string $locale = null): void
     {
         $this->setData('abbrev', $abbrev, $locale);
     }
@@ -51,7 +51,7 @@ public function getPolicy(?string $locale): string|array|null
         return $this->getData('policy', $locale);
     }
 
-    public function setPolicy(string|array $policy, string $locale = null): void
+    public function setPolicy(string|array $policy, ?string $locale = null): void
     {
         $this->setData('policy', $policy, $locale);
     }
@@ -186,7 +186,7 @@ public function getIdentifyType(?string $locale): string|array|null
     /**
      * Set string identifying type of items in this section.
      */
-    public function setIdentifyType(string|array $identifyType, string $locale = null): void
+    public function setIdentifyType(string|array $identifyType, ?string $locale = null): void
     {
         $this->setData('identifyType', $identifyType, $locale);
     }
diff --git a/pages/issue/IssueHandler.php b/pages/issue/IssueHandler.php
index 5192ee7bd06..98fc5ac767c 100644
--- a/pages/issue/IssueHandler.php
+++ b/pages/issue/IssueHandler.php
@@ -326,7 +326,7 @@ public function userCanViewGalley($request)
      * 	                                                            will be displayed.
      * @param bool                      $withSubscriptionDetails    Should include the subscription related information into the template
      */
-    public static function _setupIssueTemplate(Request $request, Issue $issue, Journal $journal = null, $showToc = false, $withSubscriptionDetails = true)
+    public static function _setupIssueTemplate(Request $request, Issue $issue, ?Journal $journal = null, $showToc = false, $withSubscriptionDetails = true)
     {
         $journal ??= $request->getJournal();
         $templateMgr = TemplateManager::getManager($request);
diff --git a/tools/resolveAgencyDuplicates.php b/tools/resolveAgencyDuplicates.php
index 59d6f1473c7..f236356723a 100644
--- a/tools/resolveAgencyDuplicates.php
+++ b/tools/resolveAgencyDuplicates.php
@@ -8,8 +8,8 @@
 
 class resolveAgencyDuplicates extends \PKP\cliTool\CommandLineTool
 {
-    private string|null $command = null;
-    private string|null $agency_name = null;
+    private ?string $command = null;
+    private ?string $agency_name = null;
     private bool $forceFlag = false;
     /**
      * List of potential agencies to choose from along with related fields for resolution.