code: function MapType(schema, opts) {
    Type.call(this);
    if (!schema.values) {
      throw new Error(f('missing map values: %j', schema));
    }
    this.valuesType = Type.forSchema(schema.values, opts);
    this._branchConstructor = this._createBranchConstructor();
    Object.freeze(this);
  }
docs: Avro map. Represented as vanilla objects.