diff --git a/.phan/config.php b/.phan/config.php
index 971ea76c44f..b8507e0953a 100644
--- a/.phan/config.php
+++ b/.phan/config.php
@@ -91,9 +91,6 @@ $cfg['exclude_analysis_directory_list'] = [
 // either in-line with @phan-suppress-next-line and similar, at block-level (via @suppress), or at
 // file-level (with @phan-file-suppress), so that it stays enabled for the rest of the codebase.
 $cfg['suppress_issue_types'] = array_merge( $cfg['suppress_issue_types'], [
-	// approximate error count: 19
-	"PhanParamReqAfterOpt", // False positives with nullables (phan issue #3159). Use real nullables
-	//after dropping HHVM
 	// approximate error count: 110
 	"PhanParamTooMany", // False positives with variargs. Unsuppress after dropping HHVM
 ] );
diff --git a/.phpcs.xml b/.phpcs.xml
index 78c8b1cfcdd..75f55f27e91 100644
--- a/.phpcs.xml
+++ b/.phpcs.xml
@@ -19,6 +19,7 @@
 		<exclude name="MediaWiki.WhiteSpace.SpaceBeforeSingleLineComment.NewLineComment" />
 		<exclude name="MediaWiki.WhiteSpace.SpaceBeforeSingleLineComment.SingleSpaceBeforeSingleLineComment" />
 		<exclude name="Squiz.Scope.MethodScope.Missing" />
+		<exclude name="MediaWiki.PHP71Features.NullableType.NotAllowed" />
 	</rule>
 	<rule ref="MediaWiki.NamingConventions.PrefixedGlobalFunctions">
 		<properties>
diff --git a/includes/CommentStore.php b/includes/CommentStore.php
index 9054e7afe8d..31b1e3064a7 100644
--- a/includes/CommentStore.php
+++ b/includes/CommentStore.php
@@ -285,7 +285,7 @@ class CommentStore {
 	 * @param bool $fallback
 	 * @return CommentStoreComment
 	 */
-	private function getCommentInternal( IDatabase $db = null, $key, $row, $fallback = false ) {
+	private function getCommentInternal( ?IDatabase $db, $key, $row, $fallback = false ) {
 		$row = (array)$row;
 		if ( array_key_exists( "{$key}_text", $row ) && array_key_exists( "{$key}_data", $row ) ) {
 			$cid = $row["{$key}_cid"] ?? null;
diff --git a/includes/api/ApiUsageException.php b/includes/api/ApiUsageException.php
index f9304527370..5d5339388b7 100644
--- a/includes/api/ApiUsageException.php
+++ b/includes/api/ApiUsageException.php
@@ -36,7 +36,7 @@ class ApiUsageException extends MWException implements ILocalizedException {
 	 * @param int $httpCode HTTP error code to use
 	 */
 	public function __construct(
-		ApiBase $module = null, StatusValue $status, $httpCode = 0
+		?ApiBase $module, StatusValue $status, $httpCode = 0
 	) {
 		if ( $status->isOK() ) {
 			throw new InvalidArgumentException( __METHOD__ . ' requires a fatal Status' );
@@ -61,7 +61,7 @@ class ApiUsageException extends MWException implements ILocalizedException {
 	 * @return static
 	 */
 	public static function newWithMessage(
-		ApiBase $module = null, $msg, $code = null, $data = null, $httpCode = 0
+		?ApiBase $module, $msg, $code = null, $data = null, $httpCode = 0
 	) {
 		return new static(
 			$module,
diff --git a/includes/changes/CategoryMembershipChange.php b/includes/changes/CategoryMembershipChange.php
index 5a7f45ea250..78ec38025b6 100644
--- a/includes/changes/CategoryMembershipChange.php
+++ b/includes/changes/CategoryMembershipChange.php
@@ -155,7 +155,7 @@ class CategoryMembershipChange {
 	private function notifyCategorization(
 		$timestamp,
 		Title $categoryTitle,
-		User $user = null,
+		?User $user,
 		$comment,
 		Title $pageTitle,
 		$lastTimestamp,
diff --git a/includes/changes/RecentChange.php b/includes/changes/RecentChange.php
index e18482505cb..a0ae348a9ea 100644
--- a/includes/changes/RecentChange.php
+++ b/includes/changes/RecentChange.php
@@ -907,7 +907,7 @@ class RecentChange implements Taggable {
 	public static function newForCategorization(
 		$timestamp,
 		Title $categoryTitle,
-		User $user = null,
+		?User $user,
 		$comment,
 		Title $pageTitle,
 		$oldRevId,
diff --git a/includes/diff/DifferenceEngine.php b/includes/diff/DifferenceEngine.php
index 6fb37c126ff..a39ca82d384 100644
--- a/includes/diff/DifferenceEngine.php
+++ b/includes/diff/DifferenceEngine.php
@@ -1662,7 +1662,7 @@ class DifferenceEngine extends ContextSource {
 	 * @param RevisionRecord $newRevision
 	 */
 	public function setRevisions(
-		RevisionRecord $oldRevision = null, RevisionRecord $newRevision
+		?RevisionRecord $oldRevision, RevisionRecord $newRevision
 	) {
 		if ( $oldRevision ) {
 			$this->mOldRev = new Revision( $oldRevision );
diff --git a/includes/export/XmlDumpWriter.php b/includes/export/XmlDumpWriter.php
index e697ef2197f..43eaf055155 100644
--- a/includes/export/XmlDumpWriter.php
+++ b/includes/export/XmlDumpWriter.php
@@ -297,14 +297,14 @@ class XmlDumpWriter {
 	 *
 	 * @param object $obj
 	 * @param string $method
-	 * @param array $args
 	 * @param string $warning The warning to output in case of a storage related exception.
+	 * @param array $args
 	 *
 	 * @return mixed Returns the method's return value,
 	 *         or null in case of a storage related exception.
 	 * @throws Exception
 	 */
-	private function invokeLenient( $obj, $method, $args = [], $warning ) {
+	private function invokeLenient( $obj, $method, $warning, $args = [] ) {
 		try {
 			return call_user_func_array( [ $obj, $method ], $args );
 		} catch ( SuppressedDataException $ex ) {
@@ -386,7 +386,6 @@ class XmlDumpWriter {
 			$sha1 = $this->invokeLenient(
 				$rev,
 				'getSha1',
-				[],
 				'failed to determine sha1 for revision ' . $rev->getId()
 			);
 			$out .= "      " . Xml::element( 'sha1', null, strval( $sha1 ) ) . "\n";
@@ -400,8 +399,8 @@ class XmlDumpWriter {
 			$content = $this->invokeLenient(
 				$rev,
 				'getContent',
-				[ SlotRecord::MAIN, RevisionRecord::RAW ],
-				'Failed to load main slot content of revision ' . $rev->getId()
+				'Failed to load main slot content of revision ' . $rev->getId(),
+				[ SlotRecord::MAIN, RevisionRecord::RAW ]
 			);
 
 			$text = $content ? $content->serialize() : '';
@@ -456,7 +455,6 @@ class XmlDumpWriter {
 			'bytes' => $this->invokeLenient(
 				$slot,
 				'getSize',
-				[],
 				'failed to determine size for slot ' . $slot->getRole() . ' of revision '
 				. $slot->getRevision()
 			) ?: '0'
@@ -466,7 +464,6 @@ class XmlDumpWriter {
 			$textAttributes['sha1'] = $this->invokeLenient(
 				$slot,
 				'getSha1',
-				[],
 				'failed to determine sha1 for slot ' . $slot->getRole() . ' of revision '
 				. $slot->getRevision()
 			) ?: '';
@@ -476,7 +473,6 @@ class XmlDumpWriter {
 			$content = $this->invokeLenient(
 				$slot,
 				'getContent',
-				[],
 				'failed to load content for slot ' . $slot->getRole() . ' of revision '
 				. $slot->getRevision()
 			);
diff --git a/includes/jobqueue/jobs/EmaillingJob.php b/includes/jobqueue/jobs/EmaillingJob.php
index 960e88288f0..4137c7b7914 100644
--- a/includes/jobqueue/jobs/EmaillingJob.php
+++ b/includes/jobqueue/jobs/EmaillingJob.php
@@ -28,7 +28,7 @@
  * @ingroup JobQueue
  */
 class EmaillingJob extends Job {
-	function __construct( Title $title = null, array $params ) {
+	function __construct( ?Title $title, array $params ) {
 		parent::__construct( 'sendMail', Title::newMainPage(), $params );
 	}
 
diff --git a/includes/libs/rdbms/exception/DBError.php b/includes/libs/rdbms/exception/DBError.php
index 6b67b45bfb7..d32412224d2 100644
--- a/includes/libs/rdbms/exception/DBError.php
+++ b/includes/libs/rdbms/exception/DBError.php
@@ -37,7 +37,7 @@ class DBError extends RuntimeException {
 	 * @param string $error A simple error message to be used for debugging
 	 * @param \Exception|\Throwable|null $prev Previous exception
 	 */
-	public function __construct( IDatabase $db = null, $error, $prev = null ) {
+	public function __construct( ?IDatabase $db, $error, $prev = null ) {
 		parent::__construct( $error, 0, $prev );
 		$this->db = $db;
 	}
diff --git a/includes/libs/rdbms/exception/DBExpectedError.php b/includes/libs/rdbms/exception/DBExpectedError.php
index 73bc1f18297..24000f4ab0a 100644
--- a/includes/libs/rdbms/exception/DBExpectedError.php
+++ b/includes/libs/rdbms/exception/DBExpectedError.php
@@ -40,7 +40,7 @@ class DBExpectedError extends DBError implements MessageSpecifier {
 	 * @param \Exception|\Throwable|null $prev
 	 */
 	public function __construct(
-		IDatabase $db = null, $error, array $params = [], $prev = null
+		?IDatabase $db, $error, array $params = [], $prev = null
 	) {
 		parent::__construct( $db, $error, $prev );
 		$this->params = $params;
diff --git a/includes/parser/Parser.php b/includes/parser/Parser.php
index 0ad62dca03a..1c821f58c60 100644
--- a/includes/parser/Parser.php
+++ b/includes/parser/Parser.php
@@ -831,7 +831,7 @@ class Parser {
 	 * @param bool|PPFrame $frame
 	 * @return mixed|string
 	 */
-	public function preprocess( $text, Title $title = null,
+	public function preprocess( $text, ?Title $title,
 		ParserOptions $options, $revid = null, $frame = false
 	) {
 		$magicScopeVariable = $this->lock();
@@ -4882,7 +4882,7 @@ class Parser {
 	 * @param bool $clearState
 	 * @param int|null $revId
 	 */
-	public function startExternalParse( Title $title = null, ParserOptions $options,
+	public function startExternalParse( ?Title $title, ParserOptions $options,
 		$outputType, $clearState = true, $revId = null
 	) {
 		$this->startParse( $title, $options, $outputType, $clearState );
@@ -4897,7 +4897,7 @@ class Parser {
 	 * @param int $outputType
 	 * @param bool $clearState
 	 */
-	private function startParse( Title $title = null, ParserOptions $options,
+	private function startParse( ?Title $title, ParserOptions $options,
 		$outputType, $clearState = true
 	) {
 		$this->setTitle( $title );
diff --git a/includes/resourceloader/ResourceLoaderWikiModule.php b/includes/resourceloader/ResourceLoaderWikiModule.php
index 237cea46c37..6fa4b1bca9f 100644
--- a/includes/resourceloader/ResourceLoaderWikiModule.php
+++ b/includes/resourceloader/ResourceLoaderWikiModule.php
@@ -531,7 +531,7 @@ class ResourceLoaderWikiModule extends ResourceLoaderModule {
 	 * @since 1.28
 	 */
 	public static function invalidateModuleCache(
-		Title $title, Revision $old = null, Revision $new = null, $domain
+		Title $title, ?Revision $old, ?Revision $new, $domain
 	) {
 		static $formats = [ CONTENT_FORMAT_CSS, CONTENT_FORMAT_JAVASCRIPT ];
 
diff --git a/includes/session/CookieSessionProvider.php b/includes/session/CookieSessionProvider.php
index 6ad00eab307..284b1188da3 100644
--- a/includes/session/CookieSessionProvider.php
+++ b/includes/session/CookieSessionProvider.php
@@ -267,6 +267,7 @@ class CookieSessionProvider extends SessionProvider {
 	 * @param bool $set Whether the cookie should be set or not
 	 * @param SessionBackend|null $backend
 	 * @param WebRequest $request
+	 * @suppress PhanParamReqAfterOpt Overridden in CentralAuth
 	 */
 	protected function setForceHTTPSCookie(
 		$set, SessionBackend $backend = null, WebRequest $request
diff --git a/includes/session/UserInfo.php b/includes/session/UserInfo.php
index f5145a3f41f..0a5a2cb4c90 100644
--- a/includes/session/UserInfo.php
+++ b/includes/session/UserInfo.php
@@ -55,7 +55,7 @@ final class UserInfo {
 	/** @var User|null */
 	private $user = null;
 
-	private function __construct( User $user = null, $verified ) {
+	private function __construct( ?User $user, $verified ) {
 		if ( $user && $user->isAnon() && !User::isUsableName( $user->getName() ) ) {
 			$this->verified = true;
 			$this->user = null;
diff --git a/includes/specials/pagers/ActiveUsersPager.php b/includes/specials/pagers/ActiveUsersPager.php
index c9c3b07f81a..827b08b8b64 100644
--- a/includes/specials/pagers/ActiveUsersPager.php
+++ b/includes/specials/pagers/ActiveUsersPager.php
@@ -55,7 +55,7 @@ class ActiveUsersPager extends UsersPager {
 	 * @param IContextSource|null $context
 	 * @param FormOptions $opts
 	 */
-	public function __construct( IContextSource $context = null, FormOptions $opts ) {
+	public function __construct( ?IContextSource $context, FormOptions $opts ) {
 		parent::__construct( $context );
 
 		$this->RCMaxAge = $this->getConfig()->get( 'ActiveUserDays' );
diff --git a/includes/specials/pagers/AllMessagesTablePager.php b/includes/specials/pagers/AllMessagesTablePager.php
index 6b8b93b90a7..56f0241fc42 100644
--- a/includes/specials/pagers/AllMessagesTablePager.php
+++ b/includes/specials/pagers/AllMessagesTablePager.php
@@ -66,7 +66,7 @@ class AllMessagesTablePager extends TablePager {
 	 * @param FormOptions $opts
 	 * @param LinkRenderer $linkRenderer
 	 */
-	public function __construct( IContextSource $context = null, FormOptions $opts,
+	public function __construct( ?IContextSource $context, FormOptions $opts,
 		LinkRenderer $linkRenderer
 	) {
 		parent::__construct( $context, $linkRenderer );
diff --git a/includes/specials/pagers/DeletedContribsPager.php b/includes/specials/pagers/DeletedContribsPager.php
index 0ff54fd442d..c9e206de62b 100644
--- a/includes/specials/pagers/DeletedContribsPager.php
+++ b/includes/specials/pagers/DeletedContribsPager.php
@@ -61,7 +61,7 @@ class DeletedContribsPager extends IndexPager {
 	 */
 	protected $mNavigationBar;
 
-	public function __construct( IContextSource $context, $target, $namespace = false,
+	public function __construct( IContextSource $context, $target, $namespace,
 		LinkRenderer $linkRenderer
 	) {
 		parent::__construct( $context, $linkRenderer );
diff --git a/includes/specials/pagers/ImageListPager.php b/includes/specials/pagers/ImageListPager.php
index 5de3ecb5550..b2c6186afbf 100644
--- a/includes/specials/pagers/ImageListPager.php
+++ b/includes/specials/pagers/ImageListPager.php
@@ -51,8 +51,8 @@ class ImageListPager extends TablePager {
 
 	protected $mTableName = 'image';
 
-	public function __construct( IContextSource $context, $userName = null, $search = '',
-		$including = false, $showAll = false, LinkRenderer $linkRenderer
+	public function __construct( IContextSource $context, $userName, $search,
+		$including, $showAll, LinkRenderer $linkRenderer
 	) {
 		$this->setContext( $context );
 
diff --git a/includes/widget/search/FullSearchResultWidget.php b/includes/widget/search/FullSearchResultWidget.php
index 7212dc0498f..153fcd6e905 100644
--- a/includes/widget/search/FullSearchResultWidget.php
+++ b/includes/widget/search/FullSearchResultWidget.php
@@ -164,7 +164,7 @@ class FullSearchResultWidget implements SearchResultWidget {
 	 *  to use the title
 	 * @return string HTML
 	 */
-	protected function generateAltTitleHtml( $msgKey, Title $title = null, $text ) {
+	protected function generateAltTitleHtml( $msgKey, ?Title $title, $text ) {
 		$inner = $title === null
 			? $text
 			: $this->linkRenderer->makeLink( $title, $text ? new HtmlArmor( $text ) : null );