Question: how to specify a property that is an enum but could also be null

[ecarey-paa]

how does one specify an enum prop that could also be null? the following does not work:

schema = {
    "type": "object",
    "properties": {
        "foo": {
            "enum": ["abc", "xyz", "null"]
        }
    }
}
validate({"foo":None},schema)

interestingly the following does?

schema = {
    "foo": {
        "enum": ["abc", "xyz", "null"]
    }
}
validate({"foo":None},schema)