[dotnet] Add nullability to Alerts (#14669)

Author: RenderMichael

dotnet/src/webdriver/Alert.cs

@@ -20,14 +20,16 @@
 using System;
 using System.Collections.Generic;
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
     /// Defines the interface through which the user can manipulate JavaScript alerts.
     /// </summary>
     internal class Alert : IAlert
     {
-        private WebDriver driver;
+        private readonly WebDriver driver;
 
         /// <summary>
         /// Initializes a new instance of the <see cref="Alert"/> class.
@@ -41,12 +43,12 @@ public Alert(WebDriver driver)
         /// <summary>
         /// Gets the text of the alert.
         /// </summary>
-        public string Text
+        public string? Text
         {
             get
             {
                 Response commandResponse = this.driver.InternalExecute(DriverCommand.GetAlertText, null);
-                return commandResponse.Value.ToString();
+                return (string?)commandResponse.Value;
             }
         }
 
@@ -70,9 +72,10 @@ public void Accept()
         /// Sends keys to the alert.
         /// </summary>
         /// <param name="keysToSend">The keystrokes to send.</param>
+        /// <exception cref="ArgumentNullException">If <paramref name="keysToSend" /> is <see langword="null"/>.</exception>
         public void SendKeys(string keysToSend)
         {
-            if (keysToSend == null)
+            if (keysToSend is null)
             {
                 throw new ArgumentNullException(nameof(keysToSend), "Keys to send must not be null.");
             }

dotnet/src/webdriver/Cookie.cs

@@ -351,14 +351,12 @@ public override string ToString()
         public override bool Equals(object obj)
         {
             // Two cookies are equal if the name and value match
-            Cookie cookie = obj as Cookie;
-
             if (this == obj)
             {
                 return true;
             }
 
-            if (cookie == null)
+            if (obj is not Cookie cookie)
             {
                 return false;
             }
@@ -368,7 +366,7 @@ public override bool Equals(object obj)
                 return false;
             }
 
-            return !(this.cookieValue != null ? !this.cookieValue.Equals(cookie.cookieValue) : cookie.Value != null);
+            return string.Equals(this.cookieValue, cookie.cookieValue);
         }
 
         /// <summary>

dotnet/src/webdriver/IAlert.cs

@@ -17,6 +17,10 @@
 // under the License.
 // </copyright>
 
+using System;
+
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
@@ -27,7 +31,7 @@ public interface IAlert
         /// <summary>
         /// Gets the text of the alert.
         /// </summary>
-        string Text { get; }
+        string? Text { get; }
 
         /// <summary>
         /// Dismisses the alert.
@@ -43,6 +47,7 @@ public interface IAlert
         /// Sends keys to the alert.
         /// </summary>
         /// <param name="keysToSend">The keystrokes to send.</param>
+        /// <exception cref="ArgumentNullException">If <paramref name="keysToSend"/> is <see langword="null"/>.</exception>
         void SendKeys(string keysToSend);
     }
 }