get(key, options) {
    if (isBsonType(key, 'ObjectId')) {
      key = key.toString();
    }

    options = options || {};
    if (options.getters === false) {
      return super.get(key);
    }
    return this.$__schemaType.applyGetters(super.get(key), this.$__parent);
  }
Overwrites native Map's `get()` function to support Mongoose getters.

@api public
@method get
@memberOf Map