RpId is not optional

Author: RenderMichael

dotnet/src/webdriver/VirtualAuth/Credential.cs

@@ -34,11 +34,11 @@ public sealed class Credential
         private readonly byte[] id;
         private readonly byte[]? userHandle;
 
-        private Credential(byte[] id, bool isResidentCredential, string? rpId, string privateKey, byte[]? userHandle, int signCount)
+        private Credential(byte[] id, bool isResidentCredential, string rpId, string privateKey, byte[]? userHandle, int signCount)
         {
             this.id = id ?? throw new ArgumentNullException(nameof(id));
             this.IsResidentCredential = isResidentCredential;
-            this.RpId = rpId;
+            this.RpId = rpId ?? throw new ArgumentNullException(nameof(rpId));
             this.PrivateKey = privateKey ?? throw new ArgumentNullException(nameof(privateKey));
             this.userHandle = userHandle;
             this.SignCount = signCount;
@@ -52,7 +52,7 @@ private Credential(byte[] id, bool isResidentCredential, string? rpId, string pr
         /// <param name="privateKey">The private Key for the credentials.</param>
         /// <param name="signCount">The signature counter for the credentials.</param>
         /// <returns>The created instance of the Credential class.</returns>
-        /// <exception cref="ArgumentNullException">If <paramref name="id"/> or <paramref name="privateKey"/> are <see langword="null"/>.</exception>
+        /// <exception cref="ArgumentNullException">If <paramref name="id"/>, <paramref name="rpId"/>, or <paramref name="privateKey"/> are <see langword="null"/>.</exception>
         public static Credential CreateNonResidentCredential(byte[] id, string rpId, string privateKey, int signCount)
         {
             return new Credential(id, false, rpId, privateKey, null, signCount);
@@ -67,7 +67,7 @@ public static Credential CreateNonResidentCredential(byte[] id, string rpId, str
         /// <param name="userHandle">The user handle associated to the credential.</param>
         /// <param name="signCount">The signature counter for the credentials.</param>
         /// <returns>The created instance of the Credential class.</returns>
-        /// <exception cref="ArgumentNullException">If <paramref name="id"/> or <paramref name="privateKey"/> are <see langword="null"/>.</exception>
+        /// <exception cref="ArgumentNullException">If <paramref name="id"/>, <paramref name="rpId"/>, or <paramref name="privateKey"/> are <see langword="null"/>.</exception>
         public static Credential CreateResidentCredential(byte[] id, string rpId, string privateKey, byte[] userHandle, int signCount)
         {
             return new Credential(id, true, rpId, privateKey, userHandle, signCount);
@@ -86,7 +86,7 @@ public static Credential CreateResidentCredential(byte[] id, string rpId, string
         /// <summary>
         /// Gets the ID of the relying party of this credential.
         /// </summary>
-        public string? RpId { get; }
+        public string RpId { get; }
 
         /// <summary>
         /// Gets the private key of the credential.
@@ -130,11 +130,7 @@ public Dictionary<string, object> ToDictionary()
 
             toReturn["credentialId"] = Base64UrlEncoder.Encode(this.id);
             toReturn["isResidentCredential"] = this.IsResidentCredential;
-            if (this.RpId is not null)
-            {
-                toReturn["rpId"] = this.RpId;
-            }
-
+            toReturn["rpId"] = this.RpId;
             toReturn["privateKey"] = this.PrivateKey;
             toReturn["signCount"] = this.SignCount;
             if (this.userHandle is not null)