anchor.diff:  
       let Create specimen = SpecimenContext(builder).Resolve(specimen)
       
  +    /// Gets the <see cref="ISpecimenBuilder"/> which create instances if the
  +    /// public Query is an instance method.
       member this.Builder = builder
  -    
  +
  +    /// <summary>
  +    /// Verifies that the return value for a Property is not null.
  +    /// </summary>
  +    /// <param name="propertyInfo">The property to verify.</param>
       override this.Verify (propertyInfo : PropertyInfo) =
           if propertyInfo = null then 
               raise <| ArgumentNullException("propertyInfo")
  
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()
      
  