refactor(php74): use null coalescing (??) and ??= operators

Signed-off-by: Thomas Vincent <thomasvincent@gmail.com>

Author: somethingwithproof

includes/arrays.php

@@ -268,9 +268,7 @@
 	$default_priority = LOG_WARNING;
 }
 
-if (!isset($step)) {
-	$step = read_config_option('poller_interval');
-}
+$step ??= read_config_option('poller_interval');
 
 switch($step) {
 	case '10':

notify_lists.php

@@ -842,7 +842,7 @@ function form_actions() {
 
 		bottom_footer();
 	} else {
-		$save = ['post' => $_POST, 'selected_items' => isset($selected_items) ? $selected_items : ''];
+		$save = ['post' => $_POST, 'selected_items' => $selected_items ?? ''];
 		api_plugin_hook_function('notify_list_form_confirm', $save);
 	}
 }
@@ -974,7 +974,7 @@ function edit() {
 		draw_edit_form(
 			[
 				'config' => [],
-				'fields' => inject_form_variables($fields_notification, (isset($list) ? $list : []))
+				'fields' => inject_form_variables($fields_notification, ($list ?? []))
 			]
 		);