diff --git a/classes/file/PublicFileManager.php b/classes/file/PublicFileManager.php
index f000880e04..ae23890535 100644
--- a/classes/file/PublicFileManager.php
+++ b/classes/file/PublicFileManager.php
@@ -24,7 +24,7 @@ class PublicFileManager extends PKPPublicFileManager
     /**
      * @copydoc PKPPublicFileManager::getContextFilesPath()
      */
-    public function getContextFilesPath($contextId)
+    public function getContextFilesPath(int $contextId)
     {
         return Config::getVar('files', 'public_files_dir') . '/contexts/' . (int) $contextId;
     }
diff --git a/classes/oai/ops/OAIDAO.php b/classes/oai/ops/OAIDAO.php
index bfbbd4549d..ef02d74ddf 100644
--- a/classes/oai/ops/OAIDAO.php
+++ b/classes/oai/ops/OAIDAO.php
@@ -58,16 +58,11 @@ public function __construct()
     /**
      * Cached function to get a server
      *
-     * @param int $serverId
-     *
      * @return object
      */
-    public function &getServer($serverId)
+    public function getServer(int $serverId)
     {
-        if (!isset($this->serverCache[$serverId])) {
-            $this->serverCache[$serverId] = $this->serverDao->getById($serverId);
-        }
-        return $this->serverCache[$serverId];
+        return $this->serverCache[$serverId] ??= $this->serverDao->getById($serverId);
     }
 
     /**
@@ -92,14 +87,14 @@ public function &getSection($sectionId)
     /**
      * Return hierarchy of OAI sets (servers plus server sections).
      *
-     * @param int $serverId
      * @param int $offset
      * @param int $total
      *
      * @return array OAISet
+     *
      * @hook OAIDAO::getServerSets [[$this, $serverId, $offset, $limit, $total, &$sets]]
      */
-    public function &getServerSets($serverId, $offset, $limit, &$total)
+    public function &getServerSets(int $serverId, $offset, $limit, &$total)
     {
         if (isset($serverId)) {
             $servers = [$this->serverDao->getById($serverId)];
diff --git a/classes/oai/ops/ServerOAI.php b/classes/oai/ops/ServerOAI.php
index 3a2e4690f3..4f2434d7a9 100644
--- a/classes/oai/ops/ServerOAI.php
+++ b/classes/oai/ops/ServerOAI.php
@@ -38,8 +38,7 @@ class ServerOAI extends OAI
     /** @var Server associated server object */
     public $server;
 
-    /** @var int|null Server ID; null if no server */
-    public $serverId;
+    public ?int $serverId;
 
     /** @var OAIDAO DAO for retrieving OAI records/tokens from database */
     public $dao;
@@ -182,6 +181,7 @@ public function record($identifier)
 
     /**
      * @copydoc OAI::records()
+     *
      * @hook ServerOAI::records [[$this, $from, $until, $set, $offset, $limit, &$total, &$records]]
      */
     public function records($metadataPrefix, $from, $until, $set, $offset, $limit, &$total)
@@ -201,6 +201,7 @@ public function records($metadataPrefix, $from, $until, $set, $offset, $limit, &
 
     /**
      * @copydoc OAI::identifiers()
+     *
      * @hook ServerOAI::identifiers [[$this, $from, $until, $set, $offset, $limit, &$total, &$records]]
      */
     public function identifiers($metadataPrefix, $from, $until, $set, $offset, $limit, &$total)
@@ -220,6 +221,7 @@ public function identifiers($metadataPrefix, $from, $until, $set, $offset, $limi
 
     /**
      * @copydoc OAI::sets()
+     *
      * @hook ServerOAI::sets [[$this, $offset, $limit, &$total, &$sets]]
      */
     public function sets($offset, $limit, &$total)
diff --git a/classes/publication/Publication.php b/classes/publication/Publication.php
index 353f98ba12..342fcc6a77 100644
--- a/classes/publication/Publication.php
+++ b/classes/publication/Publication.php
@@ -30,11 +30,9 @@ class Publication extends PKPPublication
     /**
      * Get the URL to a localized cover image
      *
-     * @param int $contextId
-     *
      * @return string
      */
-    public function getLocalizedCoverImageUrl($contextId)
+    public function getLocalizedCoverImageUrl(int $contextId)
     {
         $coverImage = $this->getLocalizedData('coverImage');
 
diff --git a/classes/section/Section.php b/classes/section/Section.php
index f6892181b3..ca149d8e73 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);
     }
@@ -230,7 +230,7 @@ public function getDescription(?string $locale): string|array|null
     /**
      * Set series description.
      */
-    public function setDescription(string|array $description, string $locale = null): void
+    public function setDescription(string|array $description, ?string $locale = null): void
     {
         $this->setData('description', $description, $locale);
     }
diff --git a/classes/server/ServerDAO.php b/classes/server/ServerDAO.php
index 33ca32ac14..1d93d6d2f1 100644
--- a/classes/server/ServerDAO.php
+++ b/classes/server/ServerDAO.php
@@ -77,12 +77,11 @@ public function getTitles($enabledOnly = false)
     /**
      * Delete the public IDs of all publishing objects in a server.
      *
-     * @param int $serverId
      * @param string $pubIdType One of the NLM pub-id-type values or
      * 'other::something' if not part of the official NLM list
      * (see <http://dtd.nlm.nih.gov/publishing/tag-library/n-4zh0.html>).
      */
-    public function deleteAllPubIds($serverId, $pubIdType)
+    public function deleteAllPubIds(int $serverId, $pubIdType)
     {
         Repo::galley()->dao->deleteAllPubIds($serverId, $pubIdType);
         Repo::submissionFile()->dao->deleteAllPubIds($serverId, $pubIdType);
@@ -93,7 +92,6 @@ public function deleteAllPubIds($serverId, $pubIdType)
      * Check whether the given public ID exists for any publishing
      * object in a server.
      *
-     * @param int $serverId
      * @param string $pubIdType One of the NLM pub-id-type values or
      * 'other::something' if not part of the official NLM list
      * (see <http://dtd.nlm.nih.gov/publishing/tag-library/n-4zh0.html>).
@@ -106,7 +104,7 @@ public function deleteAllPubIds($serverId, $pubIdType)
      * @return bool
      */
     public function anyPubIdExists(
-        $serverId,
+        int $serverId,
         $pubIdType,
         $pubId,
         $assocType = MetadataTypeDescription::ASSOC_TYPE_ANY,
diff --git a/classes/submission/DAO.php b/classes/submission/DAO.php
index 37bbba8013..41a3baa0d3 100644
--- a/classes/submission/DAO.php
+++ b/classes/submission/DAO.php
@@ -46,7 +46,7 @@ public function deleteById(int $id): int
      *
      * @return DAOResultFactory<Submission>
      */
-    public function getExportable($contextId, $pubIdType = null, $title = null, $author = null, $issueId = null, $pubIdSettingName = null, $pubIdSettingValue = null, $rangeInfo = null)
+    public function getExportable(int $contextId, $pubIdType = null, $title = null, $author = null, $issueId = null, $pubIdSettingName = null, $pubIdSettingValue = null, $rangeInfo = null)
     {
         $q = DB::table('submissions', 's')
             ->leftJoin('publications AS p', 's.current_publication_id', '=', 'p.publication_id')