message: Make birthdate optional
diff: @@ -23,7 +23,7 @@ pub struct PublicUser {
  ///[private user object](https://developer.spotify.com/web-api/object-model/#user-object-private)
  #[derive(Clone, Debug, Serialize, Deserialize)]
  pub struct PrivateUser {
  - pub birthdate: NaiveDate,
  + pub birthdate: Option<NaiveDate>,
  pub country: String,
  pub display_name: Option<String>,
  pub email: String,
  