Dear John,

"Is this the error you get when you are ordering a multilink by
an integer property?"

When the property is itself and integer, for example on
context.documents.sorted('intprop')
where 'intprop' is a property defined as intprop = Integer() in the class 'documents' pointing to, then I get (before applying any of your patches):

<class 'TypeError'>: '<' not supported between instances of 'int' and 'NoneType'.

However, if I I call 
context.documents.sorted('classprop') 
where 'classprop' is a Class() with integer order property, then I still get 

<class 'TypeError'>: '<' not supported between instances of 'NoneType' and 'str'.

I hope this agrees with your observations.