diff --git a/composer.json b/composer.json
index 322ddedbf..f3e15d565 100644
--- a/composer.json
+++ b/composer.json
@@ -3,7 +3,7 @@
 		"jakub-onderka/php-console-highlighter": "0.3.2",
 		"jakub-onderka/php-parallel-lint": "1.0.0",
 		"mediawiki/mediawiki-codesniffer": "28.0.0",
-		"mediawiki/mediawiki-phan-config": "0.8.0",
+		"mediawiki/mediawiki-phan-config": "0.9.0",
 		"mediawiki/minus-x": "0.3.2"
 	},
 	"scripts": {
diff --git a/src/Cite.php b/src/Cite.php
index 8f4576ba0..29f54858b 100644
--- a/src/Cite.php
+++ b/src/Cite.php
@@ -139,7 +139,7 @@ class Cite {
 
 	/**
 	 * @param ?string $text
-	 * @param ?string $group
+	 * @param string $group
 	 * @param ?string $name
 	 * @param ?string $extends
 	 * @param ?string $follow
@@ -148,13 +148,16 @@ class Cite {
 	 */
 	private function validateRef(
 		?string $text,
-		?string $group,
+		string $group,
 		?string $name,
 		?string $extends,
 		?string $follow,
 		?string $dir
 	) : StatusValue {
-		if ( ctype_digit( $name ) || ctype_digit( $follow ) || ctype_digit( $extends ) ) {
+		if ( ctype_digit( (string)$name )
+			|| ctype_digit( (string)$extends )
+			|| ctype_digit( (string)$follow )
+		) {
 			// Numeric names mess up the resulting id's, potentially producing
 			// duplicate id's in the XHTML.  The Right Thing To Do
 			// would be to mangle them, but it's not really high-priority
@@ -204,7 +207,7 @@ class Cite {
 			}
 		}
 
-		if ( preg_match(
+		if ( $text !== null && preg_match(
 			'/<ref(erences)?\b[^>]*+>/i',
 			preg_replace( '#<(\w++)[^>]*+>.*?</\1\s*>|<!--.*?-->#s', '', $text )
 		) ) {
@@ -230,7 +233,7 @@ class Cite {
 	private function validateRefInReferences(
 		?string $text,
 		?string $name,
-		?string $group
+		string $group
 	): StatusValue {
 		// FIXME: Some assertions make assumptions that rely on earlier tests not failing.
 		//  These dependencies need to be explicit so they aren't accidentally broken by
@@ -324,7 +327,7 @@ class Cite {
 						...$error['params']
 					);
 				}
-			} else {
+			} elseif ( $text !== null ) {
 				$groupRefs = $this->referenceStack->getGroupRefs( $group );
 				if ( !isset( $groupRefs[$name]['text'] ) ) {
 					$this->referenceStack->appendText( $group, $name, $text );
diff --git a/src/ReferenceStack.php b/src/ReferenceStack.php
index 5be9ea22b..d5f1e4082 100644
--- a/src/ReferenceStack.php
+++ b/src/ReferenceStack.php
@@ -135,7 +135,7 @@ class ReferenceStack {
 			$this->groupRefSequence[$group] = 0;
 		}
 
-		if ( $this->refs[$group][$follow] ?? false ) {
+		if ( $follow && isset( $this->refs[$group][$follow] ) ) {
 			// We know the parent note already, so just perform the "follow" and bail out
 			// TODO: Separate `pushRef` from these side-effects.
 			$this->appendText( $group, $follow, ' ' . $text );
@@ -238,6 +238,7 @@ class ReferenceStack {
 			}
 		}
 
+		// @phan-suppress-next-line PhanTypePossiblyInvalidDimOffset "key" is guaranteed to be set
 		$this->refCallStack[] = [ $action, $ref['key'], $group, $name, $extends, $text, $argv ];
 		return $ref;
 	}
@@ -395,11 +396,11 @@ class ReferenceStack {
 	/**
 	 * Return all references for a group.
 	 *
-	 * @param ?string $group
+	 * @param string $group
 	 * @return array[]
 	 */
-	public function getGroupRefs( ?string $group ) : array {
-		return $this->refs[$group ?? Cite::DEFAULT_GROUP] ?? [];
+	public function getGroupRefs( string $group ) : array {
+		return $this->refs[$group] ?? [];
 	}
 
 	/**
diff --git a/src/ReferencesFormatter.php b/src/ReferencesFormatter.php
index 1319cb9bb..b3bb7d95a 100644
--- a/src/ReferencesFormatter.php
+++ b/src/ReferencesFormatter.php
@@ -266,7 +266,7 @@ class ReferencesFormatter {
 		return $this->messageLocalizer->localizeDigits( $base ) .
 			$this->messageLocalizer->formatNum(
 				'.' .
-				str_pad( $offset, strlen( $max ), '0', STR_PAD_LEFT )
+				str_pad( (string)$offset, strlen( (string)$max ), '0', STR_PAD_LEFT )
 			);
 	}
 
diff --git a/tests/phpunit/unit/CiteUnitTest.php b/tests/phpunit/unit/CiteUnitTest.php
index 4ca9c45c9..c91dbd374 100644
--- a/tests/phpunit/unit/CiteUnitTest.php
+++ b/tests/phpunit/unit/CiteUnitTest.php
@@ -68,7 +68,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => null,
 				'name' => '1',
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => null,
@@ -80,7 +80,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 't',
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => '1',
 				'extends' => null,
 				'dir' => null,
@@ -92,7 +92,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 't',
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => '1',
 				'dir' => null,
@@ -104,7 +104,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 't',
 				'name' => 'n',
-				'group' => null,
+				'group' => '',
 				'follow' => 'f',
 				'extends' => null,
 				'dir' => null,
@@ -116,7 +116,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 't',
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => 'f',
 				'extends' => 'e',
 				'dir' => null,
@@ -129,7 +129,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 't',
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => null,
@@ -141,7 +141,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => '',
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => null,
@@ -153,7 +153,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => null,
 				'name' => null,
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => null,
@@ -165,7 +165,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 'Foo <ref name="bar">',
 				'name' => 'n',
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => null,
@@ -251,7 +251,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 'not empty',
 				'name' => 'n',
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => 'RTL',
@@ -263,7 +263,7 @@ class CiteUnitTest extends \MediaWikiUnitTestCase {
 				'isSectionPreview' => false,
 				'text' => 'not empty',
 				'name' => 'n',
-				'group' => null,
+				'group' => '',
 				'follow' => null,
 				'extends' => null,
 				'dir' => 'foobar',