Some servers does not provide A records for nameservers.
missing A record(s) for (ns1.first-ns.de,robotns2.second-ns.de,robotns3.second-ns.com) at nameserver 213.239.242.238
missing A record(s) for (ns1.first-ns.de,robotns2.second-ns.de,robotns3.second-ns.com) at nameserver 213.133.105.6
missing A record(s) for (ns1.first-ns.de,robotns2.second-ns.de,robotns3.second-ns.com) at nameserver 193.47.99.3
missing A record(s) for (ns1.first-ns.de,robotns2.second-ns.de,robotns3.second-ns.com) at nameserver 138.201.198.102