[dotnet] Fix null warnings in RelativeBy by sealing the type (#15379)

* [dotnet] Fix null warnings in `RelativeBy` by sealing the type

* minimize changes

* Address other low-hanging nullability warnings

* Seal the type explicitly

Author: RenderMichael

dotnet/src/support/Extensions/WebDriverExtensions.cs

@@ -115,7 +115,7 @@ public static void ExecuteJavaScript(this IWebDriver driver, string script, para
             }
         }
 
-        private static object ExecuteJavaScriptInternal(IWebDriver driver, string script, object?[] args)
+        private static object? ExecuteJavaScriptInternal(IWebDriver driver, string script, object?[] args)
         {
             IJavaScriptExecutor? executor = GetDriverAs<IJavaScriptExecutor>(driver)
                 ?? throw new WebDriverException("Driver does not implement IJavaScriptExecutor");

dotnet/src/support/UI/SelectElement.cs

@@ -53,7 +53,7 @@ public SelectElement(IWebElement element)
             this.WrappedElement = element;
 
             // let check if it's a multiple
-            string attribute = element.GetAttribute("multiple");
+            string? attribute = element.GetAttribute("multiple");
             this.IsMultiple = attribute != null && !attribute.Equals("false", StringComparison.OrdinalIgnoreCase);
         }
 

dotnet/src/webdriver/RelativeBy.cs

@@ -29,16 +29,13 @@ namespace OpenQA.Selenium
     /// <summary>
     /// Provides a mechanism for finding elements spatially relative to other elements.
     /// </summary>
-    public class RelativeBy : By
+    public sealed class RelativeBy : By
     {
         private readonly string wrappedAtom;
         private readonly object root;
         private readonly List<object> filters = new List<object>();
 
-        /// <summary>
-        /// Prevents a default instance of the <see cref="RelativeBy"/> class.
-        /// </summary>
-        protected RelativeBy() : base()
+        private static string GetWrappedAtom()
         {
             string atom;
             using (Stream atomStream = ResourceUtilities.GetResourceStream("find-elements.js", "find-elements.js"))
@@ -49,13 +46,13 @@ protected RelativeBy() : base()
                 }
             }
 
-            wrappedAtom = string.Format(CultureInfo.InvariantCulture, "/* findElements */return ({0}).apply(null, arguments);", atom);
+            return string.Format(CultureInfo.InvariantCulture, "/* findElements */return ({0}).apply(null, arguments);", atom);
         }
 
-        private RelativeBy(object root, List<object>? filters = null) : this()
+        private RelativeBy(object root, List<object>? filters = null)
         {
+            this.wrappedAtom = GetWrappedAtom();
             this.root = GetSerializableRoot(root);
-
             if (filters != null)
             {
                 this.filters.AddRange(filters);
@@ -73,7 +70,6 @@ public static RelativeBy WithLocator(By by)
             return new RelativeBy(by);
         }
 
-
         /// <summary>
         /// Finds the first element matching the criteria.
         /// </summary>