diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/class-walker-category.php
--- a/wp/wp-includes/class-walker-category.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/class-walker-category.php	Tue Dec 15 13:49:49 2020 +0100
@@ -53,7 +53,7 @@
 	 *                       value is 'list'. See wp_list_categories(). Default empty array.
 	 */
 	public function start_lvl( &$output, $depth = 0, $args = array() ) {
-		if ( 'list' != $args['style'] ) {
+		if ( 'list' !== $args['style'] ) {
 			return;
 		}
 
@@ -74,7 +74,7 @@
 	 *                       value is 'list'. See wp_list_categories(). Default empty array.
 	 */
 	public function end_lvl( &$output, $depth = 0, $args = array() ) {
-		if ( 'list' != $args['style'] ) {
+		if ( 'list' !== $args['style'] ) {
 			return;
 		}
 
@@ -97,11 +97,7 @@
 	 */
 	public function start_el( &$output, $category, $depth = 0, $args = array(), $id = 0 ) {
 		/** This filter is documented in wp-includes/category-template.php */
-		$cat_name = apply_filters(
-			'list_cats',
-			esc_attr( $category->name ),
-			$category
-		);
+		$cat_name = apply_filters( 'list_cats', esc_attr( $category->name ), $category );
 
 		// Don't generate an element if the category name is empty.
 		if ( '' === $cat_name ) {
@@ -143,7 +139,7 @@
 
 		$attributes = '';
 		foreach ( $atts as $attr => $value ) {
-			if ( ! empty( $value ) ) {
+			if ( is_scalar( $value ) && '' !== $value && false !== $value ) {
 				$value       = ( 'href' === $attr ) ? esc_url( $value ) : esc_attr( $value );
 				$attributes .= ' ' . $attr . '="' . $value . '"';
 			}
@@ -165,7 +161,7 @@
 			$link .= '<a href="' . esc_url( get_term_feed_link( $category->term_id, $category->taxonomy, $args['feed_type'] ) ) . '"';
 
 			if ( empty( $args['feed'] ) ) {
-				/* translators: %s: category name */
+				/* translators: %s: Category name. */
 				$alt = ' alt="' . sprintf( __( 'Feed for all posts filed under %s' ), $cat_name ) . '"';
 			} else {
 				$alt   = ' alt="' . $args['feed'] . '"';
@@ -190,7 +186,7 @@
 		if ( ! empty( $args['show_count'] ) ) {
 			$link .= ' (' . number_format_i18n( $category->count ) . ')';
 		}
-		if ( 'list' == $args['style'] ) {
+		if ( 'list' === $args['style'] ) {
 			$output     .= "\t<li";
 			$css_classes = array(
 				'cat-item',
@@ -200,8 +196,8 @@
 			if ( ! empty( $args['current_category'] ) ) {
 				// 'current_category' can be an array, so we use `get_terms()`.
 				$_current_terms = get_terms(
-					$category->taxonomy,
 					array(
+						'taxonomy'   => $category->taxonomy,
 						'include'    => $args['current_category'],
 						'hide_empty' => false,
 					)
@@ -210,6 +206,7 @@
 				foreach ( $_current_terms as $_current_term ) {
 					if ( $category->term_id == $_current_term->term_id ) {
 						$css_classes[] = 'current-cat';
+						$link          = str_replace( '<a', '<a aria-current="page"', $link );
 					} elseif ( $category->term_id == $_current_term->parent ) {
 						$css_classes[] = 'current-cat-parent';
 					}
@@ -261,7 +258,7 @@
 	 *                       to output. See wp_list_categories(). Default empty array.
 	 */
 	public function end_el( &$output, $page, $depth = 0, $args = array() ) {
-		if ( 'list' != $args['style'] ) {
+		if ( 'list' !== $args['style'] ) {
 			return;
 		}