Warnings if page options aren’t returned

For some reason I am unable to reproduce, get_option('duplicate_page_options') will sometimes return false, and generate a bunch of warnings about offset on false.

PHP Warning:  Trying to access array offset on false in /var/www/html/wp-content/plugins/duplicate-page/inc/admin-settings.php on line 60
PHP Warning:  Trying to access array offset on false in /var/www/html/wp-content/plugins/duplicate-page/inc/admin-settings.php on line 61
PHP Warning:  Trying to access array offset on false in /var/www/html/wp-content/plugins/duplicate-page/inc/admin-settings.php on line 62
...

This patch adds an empty value, and uses the WordPress native selected()

index 46d1b28..254a4e7 100644
--- a/inc/admin-settings.php
+++ b/inc/admin-settings.php
@@ -27,6 +27,14 @@ if (current_user_can('manage_options') && isset($_POST['submit_duplicate_page'])
 endif;
 
 $opt = get_option('duplicate_page_options');
+if (!is_array($opt)) {
+	$opt = array(
+            "duplicate_post_editor" => '',
+            "duplicate_post_status" => '',
+            "duplicate_post_redirect" => '',
+            "duplicate_post_suffix" => ''
+        );
+}
 if (!empty($msg) && $msg == 1):
     _e('<div class="updated settings-error notice is-dismissible" id="setting-error-settings_updated"> 
     <p><strong>Settings saved.</strong></p><button class="notice-dismiss button-custom-dismiss" type="button"><span class="screen-reader-text">Dismiss this notice</span></button></div>','duplicate-page');
@@ -46,9 +54,9 @@ endif;
 <th scope="row"><label for="duplicate_post_editor"><?php _e('Choose Editor', 'duplicate-page'); ?></label></th>
 <td>
     <select id="duplicate_post_editor" name="duplicate_post_editor">
-        <option value="all" <?php echo (isset($opt['duplicate_post_editor']) && $opt['duplicate_post_editor'] == 'all') ? "selected = 'selected'" : ''; ?>><?php _e('All Editors', 'duplicate-page'); ?></option>
-    	<option value="classic" <?php echo (isset($opt['duplicate_post_editor']) && $opt['duplicate_post_editor'] == 'classic') ? "selected = 'selected'" : ''; ?>><?php _e('Classic Editor', 'duplicate-page'); ?></option>
-    	<option value="gutenberg" <?php echo (isset($opt['duplicate_post_editor']) && $opt['duplicate_post_editor'] == 'gutenberg') ? "selected = 'selected'" : ''; ?>><?php _e('Gutenberg Editor', 'duplicate-page'); ?></option>
+       <option value="all"<?php selected($opt['duplicate_post_editor'], 'all') ?>><?php _e('All Editors', 'duplicate-page'); ?></option>
+       <option value="classic"<?php selected($opt['duplicate_post_editor'], 'classic') ?>><?php _e('Classic Editor', 'duplicate-page'); ?></option>
+       <option value="gutenberg"<?php selected($opt['duplicate_post_editor'], 'gutenberg') ?>><?php _e('Gutenberg Editor', 'duplicate-page'); ?></option>
         </select>
     <p><?php _e('Please select which editor you are using.<strong> Default: </strong> Classic Editor', 'duplicate-page'); ?></p>
 </td>
@@ -57,10 +65,10 @@ endif;
 <th scope="row"><label for="duplicate_post_status"><?php _e('Duplicate Post Status', 'duplicate-page'); ?></label></th>
 <td>
     <select id="duplicate_post_status" name="duplicate_post_status">
-    	<option value="draft" <?php echo($opt['duplicate_post_status'] == 'draft') ? "selected = 'selected'" : ''; ?>><?php _e('Draft', 'duplicate-page'); ?></option>
-    	<option value="publish" <?php echo($opt['duplicate_post_status'] == 'publish') ? "selected = 'selected'" : ''; ?>><?php _e('Publish', 'duplicate-page'); ?></option>
-    	<option value="private" <?php echo($opt['duplicate_post_status'] == 'private') ? "selected = 'selected'" : ''; ?>><?php _e('Private', 'duplicate-page'); ?></option>
-    	<option value="pending" <?php echo($opt['duplicate_post_status'] == 'pending') ? "selected = 'selected'" : ''; ?>><?php _e('Pending', 'duplicate-page'); ?></option>
+       <option value="draft"<?php selected($opt['duplicate_post_status'], 'draft') ?>><?php _e('Draft', 'duplicate-page'); ?></option>
+       <option value="publish"<?php selected($opt['duplicate_post_status'], 'publish') ?>><?php _e('Publish', 'duplicate-page'); ?></option>
+       <option value="private"<?php selected($opt['duplicate_post_status'], 'private') ?>><?php _e('Private', 'duplicate-page'); ?></option>
+       <option value="pending"<?php selected($opt['duplicate_post_status'], 'pending') ?>><?php _e('Pending', 'duplicate-page'); ?></option>
         </select>
     <p><?php _e('Please select any post status you want to assign for duplicate post.<strong> Default: </strong> Draft','duplicate-page'); ?></p>
 </td>
@@ -68,8 +76,8 @@ endif;
 <tr>
 <th scope="row"><label for="duplicate_post_redirect"><?php _e('Redirect to after click on <strong>Duplicate This Link</strong>', 'duplicate-page'); ?></label></th>
 <td><select id="duplicate_post_redirect" name="duplicate_post_redirect">
-	<option value="to_list" <?php echo($opt['duplicate_post_redirect'] == 'to_list') ? "selected = 'selected'" : ''; ?>><?php _e('To All Posts List', 'duplicate-page'); ?></option>
-	<option value="to_page" <?php echo($opt['duplicate_post_redirect'] == 'to_page') ? "selected = 'selected'" : ''; ?>><?php _e('To Duplicate Edit Screen', 'duplicate-page'); ?></option>
+       <option value="to_list"<?php selected($opt['duplicate_post_redirect'], 'to_list') ?>><?php _e('To All Posts List', 'duplicate-page'); ?></option>
+       <option value="to_page"<?php selected($opt['duplicate_post_redirect'], 'to_page') ?>><?php _e('To Duplicate Edit Screen', 'duplicate-page'); ?></option>
     </select>
     <p><?php  _e('Please select any post redirection, redirect you to selected after click on duplicate this link.<strong> Default: </strong>To All Posts List','duplicate-page'); ?></p>
 </td>