FHIR Chat · hl7 validator errors

Could you help me out understanding what's going wrong? Attached is an xml instance (source) and a to json converted instance (of test patients)

A nullFlavor extension is used on the .whenHandedOver element like this:
<whenHandedOver> <extension url="http://hl7.org/fhir/StructureDefinition/iso21090-nullFlavor"> <valueCode value="NI"/> </extension> </whenHandedOver>
This is converted to json like this:

"whenHandedOver": null,
   "_whenHandedOver": {
                    "extension": [
                        {
                            "url": "http://hl7.org/fhir/StructureDefinition/iso21090-nullFlavor",
                            "valueCode": "NI"
                        }
                    ]
                }
},

The fhir validator (FHIR Validation tool Version 4.1.60-SNAPSHOT) gives an error for the json:

Error @ Bundle.entry[1].resource.whenHandedOver (line 1, col5240) : This property must be an simple value, not a primitive property

And for XML:

Error @ Bundle.entry[1].resource.whenHandedOver (line 102, col32) : The extension http://hl7.org/fhir/StructureDefinition/iso21090-nullFlavor is not allowed to be used at this point (allowed = e:Any; this element is [[Bundle.entry.resource.whenHandedOver, BackboneElement.resource.whenHandedOver, MedicationDispense.whenHandedOver, dateTime])

I don’t know what’s going on here. Anyone an idea?

I believe the extension is used correctly.
My first attempt was to remove the null in json because that isn’t correct according to the FHIR spec. But doesn't remove the error for json and is of course not related to the xml validation error. Henegouwen.xml Henegouwen_null.json