diff --git a/includes/CategoryTree.php b/includes/CategoryTree.php
index 6ef0738c..31660a46 100644
--- a/includes/CategoryTree.php
+++ b/includes/CategoryTree.php
@@ -61,16 +61,12 @@ class CategoryTree {
 		// ensure default values and order of options.
 		// Order may become important, it may influence the cache key!
 		foreach ( $wgCategoryTreeDefaultOptions as $option => $default ) {
-			if ( isset( $options[$option] ) ) {
-				$this->mOptions[$option] = $options[$option];
-			} else {
-				$this->mOptions[$option] = $default;
-			}
+			$this->mOptions[$option] = $options[$option] ?? $default;
 		}
 
 		$this->mOptions['mode'] = self::decodeMode( $this->mOptions['mode'] );
 
-		if ( $this->mOptions['mode'] == CategoryTreeMode::PARENTS ) {
+		if ( $this->mOptions['mode'] === CategoryTreeMode::PARENTS ) {
 			// namespace filter makes no sense with CategoryTreeMode::PARENTS
 			$this->mOptions['namespaces'] = false;
 		}
@@ -82,7 +78,7 @@ class CategoryTree {
 		if ( $this->mOptions['namespaces'] ) {
 			# automatically adjust mode to match namespace filter
 			if ( count( $this->mOptions['namespaces'] ) === 1
-				&& $this->mOptions['namespaces'][0] == NS_CATEGORY ) {
+				&& $this->mOptions['namespaces'][0] === NS_CATEGORY ) {
 				$this->mOptions['mode'] = CategoryTreeMode::CATEGORIES;
 			} elseif ( !in_array( NS_FILE, $this->mOptions['namespaces'] ) ) {
 				$this->mOptions['mode'] = CategoryTreeMode::PAGES;
@@ -104,7 +100,7 @@ class CategoryTree {
 	 * @return bool
 	 */
 	private function isInverse() {
-		return $this->getOption( 'mode' ) == CategoryTreeMode::PARENTS;
+		return $this->getOption( 'mode' ) === CategoryTreeMode::PARENTS;
 	}
 
 	/**
@@ -135,7 +131,7 @@ class CategoryTree {
 
 				if ( is_numeric( $n ) ) {
 					$ns = (int)$n;
-				} elseif ( $n == '-' || $n == '_' || $n == '*' || $lower == 'main' ) {
+				} elseif ( $n === '-' || $n === '_' || $n === '*' || $lower === 'main' ) {
 					$ns = NS_MAIN;
 				} else {
 					$ns = $contLang->getNsIndex( $n );
@@ -172,15 +168,15 @@ class CategoryTree {
 			return (int)$mode;
 		}
 
-		if ( $mode == 'all' ) {
+		if ( $mode === 'all' ) {
 			$mode = CategoryTreeMode::ALL;
-		} elseif ( $mode == 'pages' ) {
+		} elseif ( $mode === 'pages' ) {
 			$mode = CategoryTreeMode::PAGES;
-		} elseif ( $mode == 'categories' || $mode == 'sub' ) {
+		} elseif ( $mode === 'categories' || $mode === 'sub' ) {
 			$mode = CategoryTreeMode::CATEGORIES;
-		} elseif ( $mode == 'parents' || $mode == 'super' || $mode == 'inverse' ) {
+		} elseif ( $mode === 'parents' || $mode === 'super' || $mode === 'inverse' ) {
 			$mode = CategoryTreeMode::PARENTS;
-		} elseif ( $mode == 'default' ) {
+		} elseif ( $mode === 'default' ) {
 			$mode = $wgCategoryTreeDefaultOptions['mode'];
 		}
 
@@ -209,15 +205,15 @@ class CategoryTree {
 			return ( (int)$value > 0 );
 		}
 
-		if ( $value == 'yes' || $value == 'y'
-			|| $value == 'true' || $value == 't' || $value == 'on'
+		if ( $value === 'yes' || $value === 'y'
+			|| $value === 'true' || $value === 't' || $value === 'on'
 		) {
 			return true;
-		} elseif ( $value == 'no' || $value == 'n'
-			|| $value == 'false' || $value == 'f' || $value == 'off'
+		} elseif ( $value === 'no' || $value === 'n'
+			|| $value === 'false' || $value === 'f' || $value === 'off'
 		) {
 			return false;
-		} elseif ( $value == 'null' || $value == 'default' || $value == 'none' || $value == 'x' ) {
+		} elseif ( $value === 'null' || $value === 'default' || $value === 'none' || $value === 'x' ) {
 			return null;
 		} else {
 			return false;
@@ -246,21 +242,21 @@ class CategoryTree {
 
 		$value = trim( strtolower( $value ) );
 
-		if ( $value == 'yes' || $value == 'y'
-			|| $value == 'true' || $value == 't' || $value == 'on'
+		if ( $value === 'yes' || $value === 'y'
+			|| $value === 'true' || $value === 't' || $value === 'on'
 		) {
 			return CategoryTreeHidePrefix::ALWAYS;
-		} elseif ( $value == 'no' || $value == 'n'
-			|| $value == 'false' || $value == 'f' || $value == 'off'
+		} elseif ( $value === 'no' || $value === 'n'
+			|| $value === 'false' || $value === 'f' || $value === 'off'
 		) {
 			return CategoryTreeHidePrefix::NEVER;
-		} elseif ( $value == 'always' ) {
+		} elseif ( $value === 'always' ) {
 			return CategoryTreeHidePrefix::ALWAYS;
-		} elseif ( $value == 'never' ) {
+		} elseif ( $value === 'never' ) {
 			return CategoryTreeHidePrefix::NEVER;
-		} elseif ( $value == 'auto' ) {
+		} elseif ( $value === 'auto' ) {
 			return CategoryTreeHidePrefix::AUTO;
-		} elseif ( $value == 'categories' || $value == 'category' || $value == 'smart' ) {
+		} elseif ( $value === 'categories' || $value === 'category' || $value === 'smart' ) {
 			return CategoryTreeHidePrefix::CATEGORIES;
 		} else {
 			return $wgCategoryTreeDefaultOptions['hideprefix'];
@@ -284,9 +280,9 @@ class CategoryTree {
 	 * @throws Exception
 	 */
 	protected static function encodeOptions( array $options, $enc ) {
-		if ( $enc == 'mode' || $enc == '' ) {
+		if ( $enc === 'mode' || $enc === '' ) {
 			$opt = $options['mode'];
-		} elseif ( $enc == 'json' ) {
+		} elseif ( $enc === 'json' ) {
 			$opt = FormatJson::encode( $options );
 		} else {
 			throw new Exception( 'Unknown encoding for CategoryTree options: ' . $enc );
@@ -300,7 +296,7 @@ class CategoryTree {
 	 * @return string
 	 */
 	public function getOptionsAsCacheKey( $depth = null ) {
-		$key = "";
+		$key = '';
 
 		foreach ( $this->mOptions as $k => $v ) {
 			if ( is_array( $v ) ) {
@@ -310,7 +306,7 @@ class CategoryTree {
 		}
 
 		if ( $depth !== null ) {
-			$key .= ";depth=" . $depth;
+			$key .= ';depth=' . $depth;
 		}
 		return $key;
 	}
@@ -402,7 +398,7 @@ class CategoryTree {
 	public function renderChildren( Title $title, $depth = 1 ) {
 		global $wgCategoryTreeMaxChildren, $wgCategoryTreeUseCategoryTable;
 
-		if ( $title->getNamespace() != NS_CATEGORY ) {
+		if ( $title->getNamespace() !== NS_CATEGORY ) {
 			// Non-categories can't have children. :)
 			return '';
 		}
@@ -436,8 +432,8 @@ class CategoryTree {
 				// NOTE: we assume that the $namespaces array contains only integers!
 				// decodeNamepsaces makes it so.
 				$where['page_namespace'] = $namespaces;
-			} elseif ( $mode != CategoryTreeMode::ALL ) {
-				if ( $mode == CategoryTreeMode::PAGES ) {
+			} elseif ( $mode !== CategoryTreeMode::ALL ) {
+				if ( $mode === CategoryTreeMode::PAGES ) {
 					$where['cl_type'] = [ 'page', 'subcat' ];
 				} else {
 					$where['cl_type'] = 'subcat';
@@ -506,13 +502,13 @@ class CategoryTree {
 
 			$cat = null;
 
-			if ( $doCount && $row->page_namespace == NS_CATEGORY ) {
+			if ( $doCount && (int)$row->page_namespace === NS_CATEGORY ) {
 				$cat = Category::newFromRow( $row, $t );
 			}
 
 			$s = $this->renderNodeInfo( $t, $cat, $depth - 1 );
 
-			if ( $row->page_namespace == NS_CATEGORY ) {
+			if ( (int)$row->page_namespace === NS_CATEGORY ) {
 				$categories .= $s;
 			} else {
 				$other .= $s;
@@ -572,7 +568,7 @@ class CategoryTree {
 	public function renderNode( Title $title, $children = 0 ) {
 		global $wgCategoryTreeUseCategoryTable;
 
-		if ( $wgCategoryTreeUseCategoryTable && $title->getNamespace() == NS_CATEGORY
+		if ( $wgCategoryTreeUseCategoryTable && $title->getNamespace() === NS_CATEGORY
 			&& !$this->isInverse()
 		) {
 			$cat = Category::newFromTitle( $title );
@@ -599,12 +595,12 @@ class CategoryTree {
 
 		$hideprefix = $this->getOption( 'hideprefix' );
 
-		if ( $hideprefix == CategoryTreeHidePrefix::ALWAYS ) {
+		if ( $hideprefix === CategoryTreeHidePrefix::ALWAYS ) {
 			$hideprefix = true;
-		} elseif ( $hideprefix == CategoryTreeHidePrefix::AUTO ) {
-			$hideprefix = ( $mode == CategoryTreeMode::CATEGORIES );
-		} elseif ( $hideprefix == CategoryTreeHidePrefix::CATEGORIES ) {
-			$hideprefix = ( $ns == NS_CATEGORY );
+		} elseif ( $hideprefix === CategoryTreeHidePrefix::AUTO ) {
+			$hideprefix = ( $mode === CategoryTreeMode::CATEGORIES );
+		} elseif ( $hideprefix === CategoryTreeHidePrefix::CATEGORIES ) {
+			$hideprefix = ( $ns === NS_CATEGORY );
 		} else {
 			$hideprefix = true;
 		}
@@ -632,11 +628,11 @@ class CategoryTree {
 
 		$attr = [ 'class' => 'CategoryTreeBullet' ];
 
-		if ( $ns == NS_CATEGORY ) {
+		if ( $ns === NS_CATEGORY ) {
 			if ( $cat ) {
-				if ( $mode == CategoryTreeMode::CATEGORIES ) {
+				if ( $mode === CategoryTreeMode::CATEGORIES ) {
 					$count = intval( $cat->getSubcatCount() );
-				} elseif ( $mode == CategoryTreeMode::PAGES ) {
+				} elseif ( $mode === CategoryTreeMode::PAGES ) {
 					$count = intval( $cat->getPageCount() ) - intval( $cat->getFileCount() );
 				} else {
 					$count = intval( $cat->getPageCount() );
@@ -646,16 +642,16 @@ class CategoryTree {
 				$bullet = '';
 				$attr['class'] = 'CategoryTreeEmptyBullet';
 			} else {
-				$linkattr = [];
+				$linkattr = [
+					'class' => 'CategoryTreeToggle',
+					'data-ct-title' => $key,
+				];
 
-				$linkattr[ 'class' ] = "CategoryTreeToggle";
-				$linkattr['data-ct-title'] = $key;
-
-				if ( $children == 0 ) {
-					$linkattr[ 'data-ct-state' ] = 'collapsed';
+				if ( $children === 0 ) {
+					$linkattr['data-ct-state'] = 'collapsed';
 				} else {
-					$linkattr[ 'data-ct-loaded' ] = true;
-					$linkattr[ 'data-ct-state' ] = 'expanded';
+					$linkattr['data-ct-loaded'] = true;
+					$linkattr['data-ct-state'] = 'expanded';
 				}
 
 				$bullet = Html::element( 'span', $linkattr ) . ' ';
@@ -677,13 +673,13 @@ class CategoryTree {
 			'div',
 			[
 				'class' => 'CategoryTreeChildren',
-				'style' => $children > 0 ? "display:block" : "display:none"
+				'style' => $children > 0 ? 'display:block' : 'display:none'
 			]
 		);
 
-		if ( $ns == NS_CATEGORY && $children > 0 ) {
+		if ( $ns === NS_CATEGORY && $children > 0 ) {
 			$children = $this->renderChildren( $title, $children );
-			if ( $children == '' ) {
+			if ( $children === '' ) {
 				switch ( $mode ) {
 					case CategoryTreeMode::CATEGORIES:
 						$msg = 'categorytree-no-subcategories';
@@ -783,7 +779,7 @@ class CategoryTree {
 		# The title must be in the category namespace
 		# Ignore a leading Category: if there is one
 		$t = Title::newFromText( $title, NS_CATEGORY );
-		if ( !$t || $t->getNamespace() != NS_CATEGORY || $t->getInterwiki() != '' ) {
+		if ( !$t || $t->getNamespace() !== NS_CATEGORY || $t->getInterwiki() !== '' ) {
 			// If we were given something like "Wikipedia:Foo" or "Template:",
 			// try it again but forced.
 			$title = "Category:$title";
diff --git a/includes/CategoryTreePage.php b/includes/CategoryTreePage.php
index 6096dac3..7e6a180a 100644
--- a/includes/CategoryTreePage.php
+++ b/includes/CategoryTreePage.php
@@ -118,10 +118,10 @@ class CategoryTreePage extends SpecialPage {
 	private function executeInputForm() {
 		$namespaces = $this->getRequest()->getVal( 'namespaces', '' );
 		// mode may be overriden by namespaces option
-		$mode = ( $namespaces == '' ? $this->getOption( 'mode' ) : CategoryTreeMode::ALL );
-		if ( $mode == CategoryTreeMode::CATEGORIES ) {
+		$mode = ( $namespaces === '' ? $this->getOption( 'mode' ) : CategoryTreeMode::ALL );
+		if ( $mode === CategoryTreeMode::CATEGORIES ) {
 			$modeDefault = 'categories';
-		} elseif ( $mode == CategoryTreeMode::PAGES ) {
+		} elseif ( $mode === CategoryTreeMode::PAGES ) {
 			$modeDefault = 'pages';
 		} else {
 			$modeDefault = 'all';
@@ -183,7 +183,7 @@ class CategoryTreePage extends SpecialPage {
 		}
 
 		$parents = $this->tree->renderParents( $title );
-		if ( $parents == '' ) {
+		if ( $parents === '' ) {
 			$parents = $this->msg( 'categorytree-no-parent-categories' )->parse();
 		}
 
diff --git a/includes/Hooks.php b/includes/Hooks.php
index c88d1702..f512e5d9 100644
--- a/includes/Hooks.php
+++ b/includes/Hooks.php
@@ -235,7 +235,7 @@ class Hooks implements
 	 * @return bool|void True or no return value to continue or false to abort
 	 */
 	public function onArticleFromTitle( $title, &$article, $context ) {
-		if ( $title->getNamespace() == NS_CATEGORY ) {
+		if ( $title->getNamespace() === NS_CATEGORY ) {
 			$article = new CategoryTreeCategoryPage( $title );
 		}
 	}
@@ -327,10 +327,7 @@ class Hooks implements
 			return;
 		}
 
-		$cat = null;
-		if ( isset( $specialPage->categoryTreeCategories[$catTitle->getDBkey()] ) ) {
-			$cat = $specialPage->categoryTreeCategories[$catTitle->getDBkey()];
-		}
+		$cat = $specialPage->categoryTreeCategories[$catTitle->getDBkey()] ?? null;
 
 		$html .= CategoryTree::createCountString( $specialPage->getContext(), $cat, 0 );
 	}