Issue: 3596. Resolve Notice with undefined index 'value' while previe…

…w order with instance payable method selected if custom offline payment method is defined in system

app/code/Magento/Payment/Helper/Data.php

@@ -293,6 +293,7 @@ public function getPaymentMethodList($sorted = true, $asLabelValue = false, $wit
             foreach ($methods as $code => $title) {
                 if (isset($groups[$code])) {
                     $labelValues[$code]['label'] = $title;
+                    $labelValues[$code]['value'] = null;
                 } elseif (isset($groupRelations[$code])) {
                     unset($labelValues[$code]);
                     $labelValues[$groupRelations[$code]]['value'][$code] = ['value' => $code, 'label' => $title];