Problem

Last weekend I tried to to access a SharePoint list items choice column value and I got a NullReferenceException. But why? Well, I created a document library and uploaded a document.

After that I created a new column using the "Document Library Settings".

Finally I had a new column. It is important to mention that I did not edit my list item after creating the new column.

Then I tried to programmatically access the list items column value by using

string myChoice = listItem[columnDisplayName].ToString();

and I got the  

NullReferenceException:
Object reference not set to an instance of an object.

Solution

You will always get a NullReferenceException until you edit the list item and select a choice value.

object myObject = listItem[columnDisplayName];

if (myObject != null)

    //DoSomething

Using the code above you can check for null. By the way: If you add a Lookup column to your list you can access the columns value by using:

SPFieldLookupValue value = new SPFieldLookupValue(listItem[columnDisplayName].ToString());

if (value.LookupValue != null)

    //DoSomething

or if you have a multiple lookup by using

SPFieldLookupValueCollection coll = new SPFieldLookupValueCollection(listItem[columnDisplayName].ToString());

foreach (SPFieldLookupValue itemValue in coll)

{

    //DoSomething

}

In this case "listItem[columnDisplayName].ToString()" doesn't throw a NullReferenceException ;)