Addition to Null Reference Exception (#10967)

Author: hawkeye101

snippets/csharp/System/NullReferenceException/Overview/example3.cs

@@ -0,0 +1,33 @@
+// <Snippet12>
+using System;
+using System.Collections.Generic;
+using System.Collections;
+using System.Runtime.Serialization;
+
+public class NullReferenceExample
+{
+    public static void Main()
+    {
+        var listType = GetListType();
+        _ = GetList(listType);
+    }
+
+    private static Type GetListType()
+    {
+        return typeof(List<int>);
+    }
+
+    private static IList GetList(Type type)
+    {
+        var emptyList = (IList)FormatterServices.GetUninitializedObject(type); // Does not call list constructor
+        var value = 1;
+        emptyList.Add(value);
+        return emptyList;
+    }
+}
+// The example displays output like the following:
+//    Unhandled Exception: System.NullReferenceException: 'Object reference
+//    not set to an instance of an object.'
+//    at System.Collections.Generic.List`1.System.Collections.IList.Add(Object item)
+//    at NullReferenceExample.GetList(Type type): line 24
+// </Snippet12>

xml/System/NullReferenceException.xml

@@ -154,6 +154,12 @@ A <xref:System.NullReferenceException> exception is thrown when you try to acces
 
      To address this issue, make sure that the argument passed to the method is not `null`, or handle the thrown exception in a `try…catch…finally` block. For more information, see [Exceptions](/dotnet/standard/exceptions/).
 
+- A list is created without knowing the type, and the list was not initialized. The `GetList` method in the following example throws the exception at the line `emptyList.Add(value)`.
+  
+     :::code language="csharp" source="~/snippets/csharp/System/NullReferenceException/Overview/example3.cs" id="Snippet12":::
+  
+     To address this issue, make sure that the list is initialized (one way to do this is to call `Activator.CreateInstance` instead of `FormatterServices.GetUninitializedObject`), or handle the thrown exception in a `try…catch…finally` block. For more information, see [Exceptions](/dotnet/standard/exceptions/).  
+
 The following Microsoft intermediate language (MSIL) instructions throw <xref:System.NullReferenceException>: `callvirt`, `cpblk`, `cpobj`, `initblk`, `ldelem.<type>`, `ldelema`, `ldfld`, `ldflda`, `ldind.<type>`, `ldlen`, `stelem.<type>`, `stfld`, `stind.<type>`, `throw`, and `unbox`.
 
 <xref:System.NullReferenceException> uses the HRESULT `COR_E_NULLREFERENCE`, which has the value 0x80004003.