I assume you mean that you get a GPF (Access violation) in 20.0?

It turns out that with the conversion to Unicode a bug sneaked in when a null has to be converted to a Variant member type in JsonToDataType. The shortest sample to reproduce it is this:

Code:
Struct tVariantCrash
    String sMember
    Variant vMember
End_Struct


Procedure Test
    tVariantCrash crash
    Handle hoJson
    Boolean bSucces
    
    Get Create (RefClass(cJsonObject)) to hoJson
    Get ParseString of hoJson '{ "sMember": "value", "vMember": null }' to bSucces
    
    Get JsonToDataType of hoJson to crash
    Send Destroy of hoJson
End_Procedure

Send Test
Of course we will make sure this gets fixed for next rev. Note that you can work around this by changing the member into a String and setting pbRequireAllMembers to false like this:



Code:
Struct tVariantCrash
    String sMember
    String vMember
End_Struct

Procedure Test
    tVariantCrash crash
    Handle hoJson
    Boolean bSucces
    
    Get Create (RefClass(cJsonObject)) to hoJson
    Set pbRequireAllMembers of hoJson to False
    Get ParseString of hoJson '{ "sMember": "value", "vMember": null }' to bSucces
    
    Get JsonToDataType of hoJson to crash
    Send Destroy of hoJson
End_Procedure

Send Test