issue using enquireLink

[davydX]

Context
try { SmppClient::$smsNullTerminateOctetstrings = false; Socket::$forceIpv4 = true; $transport = new Socket([$server->api_link], $server->port); $transport->setRecvTimeout(30000); $smppClient = new SmppClient($transport); $transport->open(); $smppClient->bindReceiver($server->username, $server->password); $isenquirelink = $smppClient->readSMS(); if (!$isenquirelink ?? false) { $smppClient->enquireLink(); }else{ //receive sms and dlr logic here } } catch (Exception $e) { $output = $e->getMessage(); }

Error

[2024-03-11 10:58:36] production.ERROR: strlen(): Argument -#1 ($string) must be of type string, null given {"exception":"[object] (TypeError(code: 0): strlen(): Argument -#1 ($string) must be of type string, null given at /.../vendor/alexandr-mironov/php8-smpp/src/Client.php:972)
[stacktrace]
-#0 /.../vendor/alexandr-mironov/php8-smpp/src/Client.php(972): strlen()
-#1 /..../vendor/alexandr-mironov/php8-smpp/src/Client.php(944): smpp\Client->sendPDU()
-#2 /.../vendor/alexandr-mironov/php8-smpp/src/Client.php(874): smpp\Client->sendCommand()
-#3 /.../myclass.php(56): smpp\Client->enquireLink()