Schema markup fatal error

Hi Scott,

The function added in the latest version (0.5.0) throws a fatal error when it is called on pages that are not product single pages, the functions try to get the global $product variable which is not available in those contexts.

Below is the corrected function, I hope to see an update soon :). The changes were:

– Added function access keyword to public
– Added documentation to the function
– Added the parameter $product which is passed by WooCommerce
– Added a double safe check to return an unchanged $markup if the product variable is not available for some reason, which is unlikely to happen as WooCommerce will only call this function if the $product variable exists.
– Removed the global $product declaration that was getting the product variable from the global context, hence why the error happened on not-product pages.

        /**
         * Adds GTIN field to product JSON-LD.
         *
         * @since       0.5.0
         * @return      array    Modified WooCommerce product structured data.
         */
        public function add_gtin_to_structured_data( $markup, $product ) {
		
	    // Bail if product variable not available
	    if ( ! $product ) { return $markup; }
			
            $product_id = $product->get_id();
            $gtin = get_post_meta( $product_id, 'hwp_product_gtin', 1 );
            $markup['gtin'] = trim($gtin);
            return $markup;
        
        }

Best,
Diego