Pulumi EKS has this interface defined:

export interface UserMapping {
    /**
     * The ARN of the IAM user to add.
     */
    userArn: pulumi.Input<aws.ARN>;
    /**
     * The user name within Kubernetes to map to the IAM user. By default, the user name is the ARN of the IAM user.
     */
    username: pulumi.Input<string>;
    /**
     * A list of groups within Kubernetes to which the user is mapped to.
     */
    groups: pulumi.Input<pulumi.Input<string>[]>;
}

Both userArn and username are required yet the docstring for username seems to indicate is filled in by default. Should username actually be optional?