[dotnet] Add nullability annotations to SessionId

dotnet/src/webdriver/SessionId.cs

@@ -17,22 +17,27 @@
 // under the License.
 // </copyright>
 
+using System;
+
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
     /// Provides a mechanism for maintaining a session for a test
     /// </summary>
-    public class SessionId
+    public class SessionId : IEquatable<SessionId>, IEquatable<string>
     {
-        private string sessionOpaqueKey;
+        private readonly string sessionOpaqueKey;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="SessionId"/> class
         /// </summary>
         /// <param name="opaqueKey">Key for the session in use</param>
+        /// <exception cref="ArgumentNullException">If <paramref name="opaqueKey"/> is <see langword="null"/>.</exception>
         public SessionId(string opaqueKey)
         {
-            this.sessionOpaqueKey = opaqueKey;
+            this.sessionOpaqueKey = opaqueKey ?? throw new ArgumentNullException(nameof(opaqueKey));
         }
 
         /// <summary>
@@ -50,24 +55,64 @@ public override string ToString()
         /// <returns>The hash code of the key</returns>
         public override int GetHashCode()
         {
-            return this.sessionOpaqueKey.GetHashCode();
+            return StringComparer.Ordinal.GetHashCode(this.sessionOpaqueKey);
+        }
+
+        /// <summary>
+        /// Indicates whether the current session ID value is the same as <paramref name="obj"/>.
+        /// </summary>
+        /// <param name="obj">The session to compare to.</param>
+        /// <returns><see langword="true"/> if the values are equal; otherwise, <see langword="false"/>.</returns>
+        public override bool Equals(object? obj)
+        {
+            return Equals(obj as SessionId);
+        }
+
+        /// <summary>
+        /// Indicates whether the current session ID value is the same as <paramref name="other"/>.
+        /// </summary>
+        /// <param name="other">A value to compare with this session ID.</param>
+        /// <returns><see langword="true"/> if the current session ID is equal to the <paramref name="other"/> parameter; otherwise, <see langword="false"/>.</returns>
+        public bool Equals(SessionId? other)
+        {
+            return other is not null && Equals(other.sessionOpaqueKey);
+        }
+
+        /// <summary>
+        /// Indicates whether the current session ID value is the same as <paramref name="other"/>.
+        /// </summary>
+        /// <param name="other">A value to compare with this session ID></param>
+        /// <returns><see langword="true"/> if the current session ID is equal to the <paramref name="other"/> parameter; otherwise, <see langword="false"/>.</returns>
+        public bool Equals(string? other)
+        {
+            return string.Equals(this.sessionOpaqueKey, other, StringComparison.Ordinal);
         }
 
         /// <summary>
-        /// Compares two Sessions
+        /// Compares the two values to determine equality.
         /// </summary>
-        /// <param name="obj">Session to compare</param>
-        /// <returns>True if they are equal or False if they are not</returns>
-        public override bool Equals(object obj)
+        /// <param name="left">The value to compare with <paramref name="right"/>.</param>
+        /// <param name="right">The value to compare with <paramref name="left"/>.</param>
+        /// <returns><see langword="true"/> if <paramref name="left"/> is equal to <paramref name="right"/>; otherwise, <see langword="false"/>.</returns>
+        public static bool operator ==(SessionId? left, SessionId? right)
         {
-            bool objectsAreEqual = false;
-            SessionId other = obj as SessionId;
-            if (other != null)
+            if (left is null)
             {
-                objectsAreEqual = this.sessionOpaqueKey.Equals(other.sessionOpaqueKey);
+                return right is null;
             }
 
-            return objectsAreEqual;
+            return left.Equals(right);
+        }
+
+        /// <summary>
+        /// Compares the two values to determine inequality.
+        /// </summary>
+        /// <param name="left">The value to compare with <paramref name="right"/>.</param>
+        /// <param name="right">The value to compare with <paramref name="left"/>.</param>
+        /// <returns><see langword="true"/> if <paramref name="left"/> is not equal to <paramref name="right"/>; otherwise, <see langword="false"/>.</returns>
+        public static bool operator !=(SessionId? left, SessionId? right)
+        {
+            return !(left == right);
         }
     }
 }

dotnet/src/webdriver/WebDriver.cs

@@ -679,7 +679,7 @@ protected void StartSession(ICapabilities capabilities)
 
             ReturnedCapabilities returnedCapabilities = new ReturnedCapabilities(rawCapabilities);
             this.capabilities = returnedCapabilities;
-            this.sessionId = new SessionId(response.SessionId);
+            this.sessionId = response.SessionId is null ? null : new SessionId(response.SessionId);
         }
 
         /// <summary>