System.ArgumentNullException: 'Value cannot be null. Paramet

Question

Hi Team

 

I have this error System.ArgumentNullException:Value cannot be null, Parameter name:connectionString.

 

 

private static string s_deviceConnectionString = Environment.GetEnvironmentVariable("IOTHUB_DEVICE-CONN_STRING"); 

 

launchSetting.json

 

{

"profiles": {

"TwinDeviceApplication": {

"commandName": "eNtsaIOTHubs",

"environmentVariables": {

"IOTHUB_DEVICE-CONN_STRING": "HostName=eNtsaIOTHubs.azure-devices.net;DeviceId=eNtsaDeviceId;SharedAccessKey=***

}

}

}

}

 

DeviceClient deviceClient = DeviceClient.CreateFromConnectionString(s_deviceClientConnectionString, s_ transportType);

 

 What am i missing? Isnt my deviceClient object has to launch this setting.json file to createConnectionString? Please assist me, thanks.