Allow null values for ts-force-gen PICKLIST enums

[saulhoward]

I would like the option to allow null values for PICKLISTs generated by ts-force-gen.

When making RestObject Updates, setting fields to null tells Salesforce to unset that field:

acc.somePicklist = null; // Type is not assignable to type:
await acc.update(); 

The above code shows a TS error because ts-force-gen generated non-nullable enums:

    public somePicklist?: PicklistConst<typeof Account.PICKLIST.somePicklist>;

ts-force-gen was run with:

"enforcePicklistValues": "ALL",
"generatePicklists": true

I see that all the other generated types are nullable, so perhaps this has been missed? Alternatively, maybe the intended behaviour of enforcePicklistValues is to omit nulls. If this is the case, it's a shame as I would like strict enums and nulls.

Many thanks for a great library!