Model = function Model(doc, fields, skipId) {
    if (!(this instanceof Model)) {
      return new Model(doc, fields, skipId);
    }
    _this.call(this, doc, fields, skipId);
  }
Subclass this model with `conn`, `schema`, and `collection` settings.

@param {Connection} conn
@param {Schema} [schema]
@param {String} [collection]
@return {Model}
@api private
@memberOf Model
@static
@method __subclass