make recurrent payment existence control work

src/Entity/Payment.php

@@ -202,11 +202,15 @@ class Payment extends BasePayment
             $reason = "Attribut détails vide ou clés absentes.";
             return null;
         }
-        $firstDayOfcreationMonth = DateTime::createFromFormat(
-            'YMd',substr($this->details,0,6) . "01"
+        $firstDayOfCreationMonth = DateTime::createFromFormat(
+            'Ymd',substr($this->details['vads_effective_creation_date'],0,6) . "01"
         );
+	if(!$firstDayOfCreationMonth) {
+	    $reason = "Error parsing vads_effective_creation_date : " . $this->details['vads_effective_creation_date'];
+	    return null;
+	}
         $day = $this->getRecurrenceMonthDay() ? $this->getRecurrenceMonthDay() - 1 : 0; //if not set assume first day of month (not a big deal anyway)
-        $dateOfFirstOccurenceAfterInitialPayment = $firstDayOfcreationMonth->modify(
+        $dateOfFirstOccurenceAfterInitialPayment = $firstDayOfCreationMonth->modify(
             $day . " days next month"
         );