VerifyIdToken Error: Null check operator used on a null value

[rayliverified]

Describe the bug
verifyIdToken throw an error if the token's sign_in_provider is null.

Null check operator used on a null value
#0      new DecodedIdToken.fromMap (package:dart_firebase_admin/src/auth/token_verifier.dart:318:48)

This is the culprit.

Line 318: signInProvider: map['sign_in_provider']! as String,

sign_in_provider can be null and is null when returned by the client's FirebaseAuth.instance.currentUser.getIdToken().

To Reproduce

1. Get a token with FirebaseAuth.instance.currentUser.getIdToken().
2. Call verifyIdToken with the token.

Expected behavior
verifyIdToken should decode successfully.