iOS EndSessionRequest without idTokenHint

Describe the bug

OIDEndSessionRequest on iOS can not be instantiated without idTokenHint.
When using an empty String as idTokenHint, the Keykloak Server shows "Session not Active" an does not destroy the session.

OIDEndSessionRequest property idTokenHint is marked es 'nullable' but not in the init-Method:

iOS API OIDEndSessionRequest:

`@property(nonatomic, readonly, nullable) NSString *idTokenHint;

• (instancetype)
  initWithConfiguration:(OIDServiceConfiguration *)configuration
  idTokenHint:(NSString *)idTokenHint
  postLogoutRedirectURL:(NSURL *)postLogoutRedirectURL
  additionalParameters:(nullable NSDictionary<NSString *, NSString *> *)additionalParameters;`

On Android, its possible to create an EndSession-Request without idToken and logout successfully on our Keykloak Server.

To Reproduce
Create EndSessionRequest in Swift
Swift API reqires to specifiy an idTokenHint
Using "" as idTokenHint
Keykloak shows "Session not Active"

Expected behavior
The OIDEndSessionRequest Initializer can be called without idTokenHint.

Screenshots

Smartphone (please complete the following information):

• Device: iOS Device
• OS: iOS15
• Browser SafariViewController
• AppAuth Version 1.4

Start with the OIDEndSessionRequest initializer declaration and its nullable idTokenHint property. Compare how the iOS request is constructed when the hint is absent with the reported empty-string case, then verify that an initializer without idTokenHint can be used for logout as expected.