diff --git a/dotnet/src/webdriver/CapabilityType.cs b/dotnet/src/webdriver/CapabilityType.cs
index bb4bf8519e4ea..c04d54ff81957 100644
--- a/dotnet/src/webdriver/CapabilityType.cs
+++ b/dotnet/src/webdriver/CapabilityType.cs
@@ -18,6 +18,9 @@
 // </copyright>
 
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+
+#nullable enable
 
 namespace OpenQA.Selenium
 {
@@ -167,7 +170,8 @@ public static class CapabilityType
         /// </summary>
         public static readonly string EnableDownloads = "se:downloadsEnabled";
 
-        private static readonly List<string> KnownSpecCompliantCapabilityNames = new List<string>() {
+        private static readonly HashSet<string> KnownSpecCompliantCapabilityNames = new HashSet<string>()
+        {
             BrowserName,
             BrowserVersion,
             PlatformName,
@@ -188,8 +192,13 @@ public static class CapabilityType
         /// <param name="capabilityName">The name of the capability to check for compliance.</param>
         /// <returns><see langword="true"/> if the capability name is valid according to the rules
         /// of the specification; otherwise, <see langword="false"/>.</returns>
-        public static bool IsSpecCompliantCapabilityName(string capabilityName)
+        public static bool IsSpecCompliantCapabilityName([NotNullWhen(true)] string? capabilityName)
         {
+            if (capabilityName is null)
+            {
+                return false;
+            }
+
             if (KnownSpecCompliantCapabilityNames.Contains(capabilityName) || capabilityName.Contains(":"))
             {
                 return true;
diff --git a/dotnet/src/webdriver/IRotatable.cs b/dotnet/src/webdriver/IRotatable.cs
index e67b0d401a9dc..02bb76c795210 100644
--- a/dotnet/src/webdriver/IRotatable.cs
+++ b/dotnet/src/webdriver/IRotatable.cs
@@ -17,6 +17,8 @@
 // under the License.
 // </copyright>
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
diff --git a/dotnet/src/webdriver/Safari/SafariOptions.cs b/dotnet/src/webdriver/Safari/SafariOptions.cs
index 25f4753ff81ad..afc38a7849efc 100644
--- a/dotnet/src/webdriver/Safari/SafariOptions.cs
+++ b/dotnet/src/webdriver/Safari/SafariOptions.cs
@@ -17,6 +17,8 @@
 // under the License.
 // </copyright>
 
+#nullable enable
+
 namespace OpenQA.Selenium.Safari
 {
     /// <summary>
@@ -46,17 +48,13 @@ public class SafariOptions : DriverOptions
         private const string EnableAutomaticInspectionSafariOption = "safari:automaticInspection";
         private const string EnableAutomaticProfilingSafariOption = "safari:automaticProfiling";
 
-        private bool enableAutomaticInspection = false;
-        private bool enableAutomaticProfiling = false;
-        private bool technologyPreview = false;
-
         /// <summary>
         /// Initializes a new instance of the <see cref="SafariOptions"/> class.
         /// </summary>
         public SafariOptions() : base()
         {
             this.BrowserName = BrowserNameValue;
-            this.technologyPreview = false;
+            this.TechnologyPreview = false;
             this.AddKnownCapabilityName(SafariOptions.EnableAutomaticInspectionSafariOption, "EnableAutomaticInspection property");
             this.AddKnownCapabilityName(SafariOptions.EnableAutomaticProfilingSafariOption, "EnableAutomaticProfiling property");
         }
@@ -66,7 +64,7 @@ public SafariOptions() : base()
         /// </summary>
         public void UseTechnologyPreview()
         {
-            this.technologyPreview = true;
+            this.TechnologyPreview = true;
             this.BrowserName = "Safari Technology Preview";
         }
 
@@ -74,30 +72,19 @@ public void UseTechnologyPreview()
         /// Gets or sets a value indicating whether to have the driver preload the
         /// Web Inspector and JavaScript debugger in the background.
         /// </summary>
-        public bool TechnologyPreview
-        {
-            get { return this.technologyPreview; }
-        }
+        public bool TechnologyPreview { get; private set; } = false;
 
         /// <summary>
         /// Gets or sets a value indicating whether to have the driver preload the
         /// Web Inspector and JavaScript debugger in the background.
         /// </summary>
-        public bool EnableAutomaticInspection
-        {
-            get { return this.enableAutomaticInspection; }
-            set { this.enableAutomaticInspection = value; }
-        }
+        public bool EnableAutomaticInspection { get; set; } = false;
 
         /// <summary>
         /// Gets or sets a value indicating whether to have the driver preload the
         /// Web Inspector and start a timeline recording in the background.
         /// </summary>
-        public bool EnableAutomaticProfiling
-        {
-            get { return this.enableAutomaticProfiling; }
-            set { this.enableAutomaticProfiling = value; }
-        }
+        public bool EnableAutomaticProfiling { get; set; } = false;
 
         /// <summary>
         /// Returns ICapabilities for Safari with these options included as
@@ -108,12 +95,12 @@ public bool EnableAutomaticProfiling
         public override ICapabilities ToCapabilities()
         {
             IWritableCapabilities capabilities = this.GenerateDesiredCapabilities(true);
-            if (this.enableAutomaticInspection)
+            if (this.EnableAutomaticInspection)
             {
                 capabilities.SetCapability(EnableAutomaticInspectionSafariOption, true);
             }
 
-            if (this.enableAutomaticProfiling)
+            if (this.EnableAutomaticProfiling)
             {
                 capabilities.SetCapability(EnableAutomaticProfilingSafariOption, true);
             }
diff --git a/dotnet/src/webdriver/ScreenOrientation.cs b/dotnet/src/webdriver/ScreenOrientation.cs
index fb496b4703c9b..1d23b2e0bc9f3 100644
--- a/dotnet/src/webdriver/ScreenOrientation.cs
+++ b/dotnet/src/webdriver/ScreenOrientation.cs
@@ -17,6 +17,8 @@
 // under the License.
 // </copyright>
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
diff --git a/dotnet/src/webdriver/WebDriverError.cs b/dotnet/src/webdriver/WebDriverError.cs
index 5811d924f53cb..f4a139cac505b 100644
--- a/dotnet/src/webdriver/WebDriverError.cs
+++ b/dotnet/src/webdriver/WebDriverError.cs
@@ -17,8 +17,11 @@
 // under the License.
 // </copyright>
 
+using System;
 using System.Collections.Generic;
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
@@ -167,54 +170,52 @@ internal static class WebDriverError
         /// </summary>
         public const string UnsupportedOperation = "unsupported operation";
 
-        private static readonly Dictionary<string, WebDriverResult> resultMap;
-
-        static WebDriverError()
+        private static readonly Dictionary<string, WebDriverResult> resultMap = new Dictionary<string, WebDriverResult>
         {
-            resultMap = new Dictionary<string, WebDriverResult>();
-            resultMap[ElementClickIntercepted] = WebDriverResult.ElementClickIntercepted;
-            resultMap[ElementNotInteractable] = WebDriverResult.ElementNotInteractable;
-            resultMap[InsecureCertificate] = WebDriverResult.InsecureCertificate;
-            resultMap[InvalidArgument] = WebDriverResult.InvalidArgument;
-            resultMap[InvalidCookieDomain] = WebDriverResult.InvalidCookieDomain;
-            resultMap[InvalidElementState] = WebDriverResult.InvalidElementState;
-            resultMap[InvalidSelector] = WebDriverResult.InvalidSelector;
-            resultMap[InvalidSessionId] = WebDriverResult.NoSuchDriver;
-            resultMap[JavaScriptError] = WebDriverResult.UnexpectedJavaScriptError;
-            resultMap[MoveTargetOutOfBounds] = WebDriverResult.MoveTargetOutOfBounds;
-            resultMap[NoSuchAlert] = WebDriverResult.NoAlertPresent;
-            resultMap[NoSuchCookie] = WebDriverResult.NoSuchCookie;
-            resultMap[NoSuchElement] = WebDriverResult.NoSuchElement;
-            resultMap[NoSuchFrame] = WebDriverResult.NoSuchFrame;
-            resultMap[NoSuchWindow] = WebDriverResult.NoSuchWindow;
-            resultMap[NoSuchShadowRoot] = WebDriverResult.NoSuchShadowRoot;
-            resultMap[ScriptTimeout] = WebDriverResult.AsyncScriptTimeout;
-            resultMap[SessionNotCreated] = WebDriverResult.SessionNotCreated;
-            resultMap[StaleElementReference] = WebDriverResult.ObsoleteElement;
-            resultMap[DetachedShadowRoot] = WebDriverResult.DetachedShadowRoot;
-            resultMap[Timeout] = WebDriverResult.Timeout;
-            resultMap[UnableToSetCookie] = WebDriverResult.UnableToSetCookie;
-            resultMap[UnableToCaptureScreen] = WebDriverResult.UnableToCaptureScreen;
-            resultMap[UnexpectedAlertOpen] = WebDriverResult.UnexpectedAlertOpen;
-            resultMap[UnknownCommand] = WebDriverResult.UnknownCommand;
-            resultMap[UnknownError] = WebDriverResult.UnknownError;
-            resultMap[UnknownMethod] = WebDriverResult.UnknownMethod;
-            resultMap[UnsupportedOperation] = WebDriverResult.UnsupportedOperation;
-        }
+            { ElementClickIntercepted, WebDriverResult.ElementClickIntercepted },
+            { ElementNotInteractable, WebDriverResult.ElementNotInteractable },
+            { InsecureCertificate, WebDriverResult.InsecureCertificate },
+            { InvalidArgument, WebDriverResult.InvalidArgument },
+            { InvalidCookieDomain, WebDriverResult.InvalidCookieDomain },
+            { InvalidElementState, WebDriverResult.InvalidElementState },
+            { InvalidSelector, WebDriverResult.InvalidSelector },
+            { InvalidSessionId, WebDriverResult.NoSuchDriver },
+            { JavaScriptError, WebDriverResult.UnexpectedJavaScriptError },
+            { MoveTargetOutOfBounds, WebDriverResult.MoveTargetOutOfBounds },
+            { NoSuchAlert, WebDriverResult.NoAlertPresent },
+            { NoSuchCookie, WebDriverResult.NoSuchCookie },
+            { NoSuchElement, WebDriverResult.NoSuchElement },
+            { NoSuchFrame, WebDriverResult.NoSuchFrame },
+            { NoSuchWindow, WebDriverResult.NoSuchWindow },
+            { NoSuchShadowRoot, WebDriverResult.NoSuchShadowRoot },
+            { ScriptTimeout, WebDriverResult.AsyncScriptTimeout },
+            { SessionNotCreated, WebDriverResult.SessionNotCreated },
+            { StaleElementReference, WebDriverResult.ObsoleteElement },
+            { DetachedShadowRoot, WebDriverResult.DetachedShadowRoot },
+            { Timeout, WebDriverResult.Timeout },
+            { UnableToSetCookie, WebDriverResult.UnableToSetCookie },
+            { UnableToCaptureScreen, WebDriverResult.UnableToCaptureScreen },
+            { UnexpectedAlertOpen, WebDriverResult.UnexpectedAlertOpen },
+            { UnknownCommand, WebDriverResult.UnknownCommand },
+            { UnknownError, WebDriverResult.UnknownError },
+            { UnknownMethod, WebDriverResult.UnknownMethod },
+            { UnsupportedOperation, WebDriverResult.UnsupportedOperation }
+        };
 
         /// <summary>
         /// Converts a string error to a <see cref="WebDriverResult"/> value.
         /// </summary>
         /// <param name="error">The error string to convert.</param>
         /// <returns>The converted <see cref="WebDriverResult"/> value.</returns>
+        /// <exception cref="ArgumentNullException">If <paramref name="error"/> is <see langword="null"/>.</exception>
         public static WebDriverResult ResultFromError(string error)
         {
-            if (!resultMap.ContainsKey(error))
+            if (!resultMap.TryGetValue(error, out WebDriverResult result))
             {
-                error = UnsupportedOperation;
+                return WebDriverResult.UnsupportedOperation;
             }
 
-            return resultMap[error];
+            return result;
         }
     }
 }
diff --git a/dotnet/src/webdriver/WebDriverResult.cs b/dotnet/src/webdriver/WebDriverResult.cs
index a18dcce7c6a42..03b9b20a83f3e 100644
--- a/dotnet/src/webdriver/WebDriverResult.cs
+++ b/dotnet/src/webdriver/WebDriverResult.cs
@@ -19,6 +19,8 @@
 
 using System;
 
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>
diff --git a/dotnet/src/webdriver/WindowType.cs b/dotnet/src/webdriver/WindowType.cs
index 2b4f3b8e2bc9f..7e1200d7b9f8e 100644
--- a/dotnet/src/webdriver/WindowType.cs
+++ b/dotnet/src/webdriver/WindowType.cs
@@ -17,6 +17,9 @@
 // under the License.
 // </copyright>
 
+
+#nullable enable
+
 namespace OpenQA.Selenium
 {
     /// <summary>