Fix crash when the user saves Mini Cart Template (#6613)

Author: gigitux

src/Templates/MiniCartTemplate.php

@@ -0,0 +1,13 @@
+<?php
+namespace Automattic\WooCommerce\Blocks\Templates;
+
+/**
+ * MiniCartTemplate class.
+ *
+ * @internal
+ */
+class MiniCartTemplate {
+
+	const SLUG = 'mini-cart';
+
+}

src/Utils/BlockTemplateUtils.php

@@ -3,6 +3,7 @@
 
 use Automattic\WooCommerce\Blocks\Templates\ProductSearchResultsTemplate;
 use Automattic\WooCommerce\Blocks\Domain\Services\FeatureGating;
+use Automattic\WooCommerce\Blocks\Templates\MiniCartTemplate;
 
 /**
  * Utility methods used for serving block templates from WooCommerce Blocks.
@@ -283,6 +284,7 @@ public static function get_block_template_description( $template_slug ) {
 		if ( isset( $plugin_template_types[ $template_slug ] ) ) {
 			return $plugin_template_types[ $template_slug ]['description'];
 		}
+		return '';
 	}
 
 	/**
@@ -313,6 +315,10 @@ public static function get_plugin_block_template_types() {
 				'title'       => _x( 'Product Search Results', 'Template name', 'woo-gutenberg-products-block' ),
 				'description' => __( 'Template used to display search results for products.', 'woo-gutenberg-products-block' ),
 			),
+			MiniCartTemplate::SLUG             => array(
+				'title'       => _x( 'Mini Cart', 'Template name', 'woo-gutenberg-products-block' ),
+				'description' => __( 'Template used to display the Mini Cart drawer.', 'woo-gutenberg-products-block' ),
+			),
 		);
 
 		return $plugin_template_types;