Add null checks and private variables for to address PHP notices and …

…deprecations

Added null checks in `function-coauthors.php` and `class-components.php` to prevent possible undefined behaviour when handling non-initialized variables. This makes the code more robust and resilient to potential errors. Moreover, added private string variables in `test-class-table.php` and private `Admin_Apple_Themes` variable to the `test-class-admin-apple-themes.php` which improves the readability and structure of these files.

includes/apple-exporter/builders/class-components.php

@@ -526,6 +526,10 @@ private function get_components_from_node( $node ) {
 	 */
 	private function get_image_full_size_url( $url ) {
 
+		if(null === $url) {
+			return '';
+		}
+
 		// Strip URL formatting for easier matching.
 		$url = urldecode( $url );
 

tests/admin/test-class-admin-apple-themes.php

@@ -16,6 +16,7 @@
  * A class which is used to test the Admin_Apple_Themes class.
  */
 class Admin_Apple_Themes_Test extends Apple_News_Testcase {
+	private Admin_Apple_Themes $themes;
 
 	/**
 	 * A helper function to create the default theme.

tests/apple-exporter/components/test-class-table.php

@@ -18,6 +18,8 @@
  * @subpackage Tests
  */
 class Apple_News_Table_Test extends Apple_News_Component_TestCase {
+	private string $html;
+	private string $html_caption;
 
 	/**
 	 * A fixture containing operations to be run before each test.

tests/mocks/function-coauthors.php

@@ -29,6 +29,10 @@ function coauthors( $between = ', ', $between_last = ' and ', $before = '', $aft
 	// Get last index.
 	$last_index = count( $apple_news_coauthors ) - 1;
 
+	if(null === $between) {
+		$between = ', ';
+	}
+
 	// Compute output.
 	$output = $before
 		. implode( $between, array_slice( $apple_news_coauthors, 0, $last_index ) )