Merge branch 'pr/16871'

includes/admin/meta-boxes/views/html-product-data-panel.php

@@ -32,7 +32,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 
 	<ul class="product_data_tabs wc-tabs">
 		<?php foreach ( self::get_product_data_tabs() as $key => $tab ) : ?>
-			<li class="<?php echo $key; ?>_options <?php echo $key; ?>_tab <?php echo implode( ' ' , (array) $tab['class'] ); ?>">
+			<li class="<?php echo $key; ?>_options <?php echo $key; ?>_tab <?php echo isset( $tab['class'] ) ? implode( ' ' , (array) $tab['class'] ) : ''; ?>">
 				<a href="#<?php echo $tab['target']; ?>"><span><?php echo esc_html( $tab['label'] ); ?></span></a>
 			</li>
 		<?php endforeach; ?>