public class lll {
public string errormessage;
 public void Login()
    {
        
        ErrorMessage='';
       final string baseUrl = 'http://dskvapconsultancyservices.createsend.com/'; 
        final string username = '05b88f78dfc4f00ce93553a79be93d04'; 
        final string password = 'rajesh12';
       
  string apikey='05b88f78dfc4f00ce93553a79be93d04';
     Blob headerValue = Blob.valueOf(username + ':' + password);
     String authorizationHeader = 'BASIC ' +
     EncodingUtil.base64Encode(headerValue);
     req.setHeader('Host','http://dskvapconsultancyservices.createsend.com/');

    req.setHeader('Authorization',authorizationHeader);
  //req.setHeader('content-type', 'text/xml;charset=utf-8');
  //req.setHeader('Content-Length','1024');
  //req.setHeader('Host','http://dskvapconsultancyservices.createsend.com/');
  //req.setHeader('Connection','keep-alive');
        
        Http h = new Http();
        HttpRequest req = new HttpRequest();
        req.setMethod('GET');
        //req.setEndpoint(baseUrl + '?loginType=&un='+username+'&pw='+password);
       //req.setEndpoint('http://api.createsend.com/05b88f78dfc4f00ce93553a79be93d04/v3/clients/clients.xml');
        req.setEndPoint('http://api.createsend.com/api/v3/clients.xml?='+apikey);
        //req.setbody('http://api.createsend.com/api/v3/clients.xml');
    
        
        HttpResponse res = h.send(req);
         //req.setEndpoint(baseUrl + 'apex/UploadFile_DifferentOrg');
           
           res = h.send(req);
           system.debug('********'+res.getbody());
           if (res.getBody().indexOf('success=true')>-1)
           {
              system.debug('Success');
           }  
        }
}

 HI I am using this code to connect campaign monitor 

bit i am getting error  that null pointer defference

please let me know the actual way to headers and endpoint and body 

please expain how to set and what to set in headers for basic authorization

thank you in advance