anchor.diff:          if (getMethod <> null) then 
               this.Verify(propertyInfo.GetGetMethod());
   
  +    /// <summary>
  +    /// Verifies that the return value for a method is not null.
  +    /// </summary>
  +    /// <remarks>
  +    /// <param name="methodInfo">The method to verify.</param>
       override this.Verify (methodInfo : MethodInfo) =
           if methodInfo = null then 
               raise <| ArgumentNullException("methodInfo")
  
positive.code:                             "The method "
                              + methodInfo.Name
                              + " returns null which is never an acceptable return"
                              + " value for a public Query (method that returns a value).")
              | _  -> Exercise methodInfo owner parameters |> ignore
negative.code: open System
  open System.Reflection
  
  /// <summary>
  /// Encapsulates a unit test verifying that the return value for a public Query
  /// (a method that returns a value) is not null.
  /// </summary>
  type ReturnValueMustNotBeNullAssertion (builder) =
      inherit IdiomaticAssertion()
      
  