Why am I getting "Object reference not set to an instance of an object" here?

Question

The following is my code:

DirectorySearcher search = new DirectorySearcher( directory );

search.Filter = "(&(objectCategory=person)(objectClass=user)(!userAccountControl:1.2.840.113556.1.4.803:=2)(|(sn=*)))";
search.PropertiesToLoad.Add( "GivenName" );
search.PropertiesToLoad.Add( "OfficePhone" );
search.PropertiesToLoad.Add( "EmployeeNumber" );


SearchResultCollection results = search.FindAll();

int thisCount = results.Count;
string filePath = "C:\\test.csv";

string contents = string.Empty;
int counter = 0;
foreach( SearchResult result in results ) {
  DirectoryEntry userEntry = result.GetDirectoryEntry();

  string givenName = userEntry.Properties[ "userPrincipalName" ].Value.ToString();
  string employeeNumber = userEntry.Properties[ "EmployeeNumber" ].Value.ToString();
  string phoneNumber = userEntry.Properties[ "OfficePhone" ].Value.ToString();

  counter = counter + 1;
}
System.IO.File.WriteAllText( filePath, contents );

The problem that I seem to not be able to get around is that when I start looping through the "results" object, the code blows up after givenName has been assigned. The error I get is:

Object reference not set to an instance of an object.

I've tried to figure out how to assign this properly but I keep running into a wall with it. Any suggestions would be greatly appreciated. I'm pretty sure it has to do with me not understanding DirectorySearcher/DirectoryEntry correctly - but I could be wrong. :-)

Answer 1

Based on this statement:

the code blows up after givenName has been assigned...

this line of code:

userEntry.Properties[ "EmployeeNumber" ]

is blowing up and letting you know that there is no property named EmployeeNumber or that the Value of EmployeeNumber is null. I'm going to bet on the second and so change that line to this:

userEntry.Properties[ "EmployeeNumber" ] as string;

and your employeeNumber field will be set to null when it is null but it won't throw an exception.