Mandatory Coupon Code

i have try to do this solutions:
https://stackoverflow.com/questions/27526677/making-the-coupon-field-mandatory-on-woocommerce/29297000#29297000

but if i don’t enter the coupon code I am redirected to ../checkout and the page is blank..

OK i have found the solutions
It is replaced in the functions.php code shown in the above solution (https://stackoverflow.com/questions/27526677/making-the-coupon-field-mandatory-on-woocommerce/29297000#29297000) , the string:
“$woocommerce->add_error(“Please enter coupon code to checkout.”);”

with

“wc_add_notice( ‘‘ . $btn[‘label’] . ‘ ‘ . __( ‘is a required field.’, ‘woocommerce’ ), ‘error’ );”