Fix salesagility#10425 - Value of "currency_id" in custom table chang…

…es from NULL to an empty string when saving

modules/DynamicFields/DynamicField.php

@@ -446,6 +446,10 @@ public function save($isUpdate)
                     continue;
                 }
 
+                if (($field['type'] === 'currency_id' && empty($this->bean->$name))) {
+                    continue;
+                }
+
                 if (!empty($this->bean->bean_fields_to_save) && !in_array($name, $this->bean->bean_fields_to_save, true)){
                     continue;
                 }