protected internal virtual void VisitNot(JsonSchemaNot constraint)
        {
            // visit self
            VisitConstraint(constraint);

            // visit children
            Visit(constraint.Not);
        }
 protected internal override void VisitNot(JsonSchemaNot constraint)
 {
     writer.WriteStartObject(Keys.Not);
     base.VisitNot(constraint);
     writer.WriteEndObject();
 }