Connect WPA2 Enterprise wifi programmatically

I am trying to connect wpa2 enterprise wifi using iPhone app programmatically.

before that I tried connecting to that wifi manually:

1. From Settings in iPhone device
2. Used these three parameters SSID, Username, password
3. After that it ask to trust the certificate and trusting the certificate, the wifi get connect, Done!

Now I am trying to connect wifi programmatically using following code:

NEHotspotEAPSettings *settings = [[NEHotspotEAPSettings alloc]init]; 
settings.password = self.password.text; 
settings.username = self.username.text; 
settings.supportedEAPTypes = [NSArray arrayWithObjects:[NSNumber numberWithInteger:NEHotspotConfigurationEAPTypeEAPPEAP], nil]; 
NEHotspotConfiguration *configuration = [[NEHotspotConfiguration alloc]initWithSSID:self.ssid.text eapSettings:settings]; 
[[NEHotspotConfigurationManager sharedManager]applyConfiguration:configuration completionHandler:^(NSError * _Nullable error) { 
if (error) {  
  NSLog(@"Error: %@",error.localizedDescription); } 
else { NSLog(@“Connected”); }
}];

but this code gives an error

Invalid EAP settings : NEHotspotConfiguration EAP settings must have either trusted server certificates or trusted server names configured

Since I don’t have any trusted server certificate or trusted server name. What should I set in the blow property of NEHotspotEAPSettings (passing nil also gives me same error)

settings.trustedServerNames

Please help to solve this. Thanks!