Taxonomy: Make sure wp_list_categories() correctly outputs term nam…

…e of `0`.

Props joyously, SergeyBiryukov.
Merges [43605] to the 5.0 branch.
Fixes #44872.

git-svn-id: https://develop.svn.wordpress.org/branches/5.0@43712 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-walker-category.php

@@ -99,7 +99,7 @@ public function start_el( &$output, $category, $depth = 0, $args = array(), $id
 		);
 
 		// Don't generate an element if the category name is empty.
-		if ( ! $cat_name ) {
+		if ( '' === $cat_name ) {
 			return;
 		}
 

tests/phpunit/tests/category/wpListCategories.php

@@ -87,6 +87,35 @@ public function test_should_not_create_element_when_cat_name_is_filtered_to_empt
 		$this->assertNotContains( 'Test Cat 1', $found );
 	}
 
+	public function list_cats_callback( $cat ) {
+		if ( 'Test Cat 1' === $cat ) {
+			return '';
+		}
+
+		return $cat;
+	}
+
+	/**
+	 * @ticket 44872
+	 */
+	public function test_should_create_element_when_cat_name_is_zero() {
+		$c = self::factory()->category->create(
+			array(
+				'name' => '0',
+			)
+		);
+
+		$found = wp_list_categories(
+			array(
+				'hide_empty' => false,
+				'echo'       => false,
+			)
+		);
+
+		$this->assertContains( "cat-item-$c", $found );
+		$this->assertContains( '0', $found );
+	}
+
 	public function test_show_option_all_link_should_go_to_home_page_when_show_on_front_is_false() {
 		$cats = self::factory()->category->create_many( 2 );
 
@@ -207,14 +236,6 @@ public function test_show_option_all_link_should_link_to_post_archive_if_no_asso
 		$this->assertContains( "<li class='cat-item-all'><a href='" . $url . "'>All</a></li>", $found );
 	}
 
-	public function list_cats_callback( $cat ) {
-		if ( 'Test Cat 1' === $cat ) {
-			return '';
-		}
-
-		return $cat;
-	}
-
 	/**
 	 * @ticket 33460
 	 */