Check for undefined params before using (#5234)

Author: bborman22

changelog/fix-woopay-params-undefined

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+
+Fix an undefined variable bug in WooPay Express Checkout.

client/checkout/platform-checkout/express-button/utils.js

@@ -4,8 +4,12 @@
  * Retrieves a configuration value.
  *
  * @param {string} name The name of the config parameter.
- * @return {*}         The value of the parameter of null.
+ * @return {*}          The value of the parameter or undefined.
  */
 export const getWooPayExpressData = ( name ) => {
+	if ( 'undefined' === typeof wcpayWooPayExpressParams ) {
+		return undefined;
+	}
+
 	return wcpayWooPayExpressParams?.[ name ];
 };