[dotnet] Annotate nullability on more of WebElement (#15230)

* [dotnet] Annotate nullability on more of `WebElement`

* Handle nullability of GetCssValue

* Implement nullability on more of `WebElement`

* fix typo

* improve error message

* Use new `EnsureValueIsNotNull` hlper

Author: RenderMichael

dotnet/src/webdriver/WebElement.cs

@@ -40,6 +40,8 @@ public class WebElement : IWebElement, IFindsElement, IWrapsDriver, ILocatable,
         /// </summary>
         public const string ElementReferencePropertyName = "element-6066-11e4-a52e-4f735466cecf";
 
+#nullable enable
+
         private readonly WebDriver driver;
 
         /// <summary>
@@ -77,7 +79,8 @@ public virtual string TagName
 
                 Response commandResponse = this.Execute(DriverCommand.GetElementTagName, parameters);
 
-                return commandResponse.Value.ToString();
+                commandResponse.EnsureValueIsNotNull();
+                return commandResponse.Value.ToString()!;
             }
         }
 
@@ -95,7 +98,8 @@ public virtual string Text
 
                 Response commandResponse = this.Execute(DriverCommand.GetElementText, parameters);
 
-                return commandResponse.Value.ToString();
+                commandResponse.EnsureValueIsNotNull();
+                return commandResponse.Value.ToString()!;
             }
         }
 
@@ -151,7 +155,11 @@ public virtual Point Location
 
                 Response commandResponse = this.Execute(DriverCommand.GetElementRect, parameters);
 
-                Dictionary<string, object> rawPoint = (Dictionary<string, object>)commandResponse.Value;
+                if (commandResponse.Value is not Dictionary<string, object?> rawPoint)
+                {
+                    throw new WebDriverException($"GetElementRect command was successful, but response was not an object: {commandResponse.Value}");
+                }
+
                 int x = Convert.ToInt32(rawPoint["x"], CultureInfo.InvariantCulture);
                 int y = Convert.ToInt32(rawPoint["y"], CultureInfo.InvariantCulture);
                 return new Point(x, y);
@@ -171,7 +179,11 @@ public virtual Size Size
 
                 Response commandResponse = this.Execute(DriverCommand.GetElementRect, parameters);
 
-                Dictionary<string, object> rawSize = (Dictionary<string, object>)commandResponse.Value;
+                if (commandResponse.Value is not Dictionary<string, object?> rawSize)
+                {
+                    throw new WebDriverException($"GetElementRect command was successful, but response was not an object: {commandResponse.Value}");
+                }
+
                 int width = Convert.ToInt32(rawSize["width"], CultureInfo.InvariantCulture);
                 int height = Convert.ToInt32(rawSize["height"], CultureInfo.InvariantCulture);
                 return new Size(width, height);
@@ -207,7 +219,7 @@ public virtual Point LocationOnScreenOnceScrolledIntoView
         {
             get
             {
-                object scriptResponse = this.driver.ExecuteScript("var rect = arguments[0].getBoundingClientRect(); return {'x': rect.left, 'y': rect.top};", this);
+                object scriptResponse = this.driver.ExecuteScript("var rect = arguments[0].getBoundingClientRect(); return {'x': rect.left, 'y': rect.top};", this)!;
 
                 Dictionary<string, object> rawLocation = (Dictionary<string, object>)scriptResponse;
 
@@ -229,7 +241,8 @@ public virtual string ComputedAccessibleLabel
 
                 Response commandResponse = this.Execute(DriverCommand.GetComputedAccessibleLabel, parameters);
 
-                return commandResponse.Value.ToString();
+                commandResponse.EnsureValueIsNotNull();
+                return commandResponse.Value.ToString()!;
             }
         }
 
@@ -240,16 +253,18 @@ public virtual string ComputedAccessibleRole
         {
             get
             {
-                // TODO: Returning this as a string is incorrect. The W3C WebDriver Specification
-                // needs to be updated to more thoroughly document the structure of what is returned
-                // by this command. Once that is done, a type-safe class will be created, and will
-                // be returned by this property.
                 Dictionary<string, object> parameters = new Dictionary<string, object>();
                 parameters.Add("id", this.Id);
 
                 Response commandResponse = this.Execute(DriverCommand.GetComputedAccessibleRole, parameters);
 
+#nullable disable
+                // TODO: Returning this as a string is incorrect. The W3C WebDriver Specification
+                // needs to be updated to more thoroughly document the structure of what is returned
+                // by this command. Once that is done, a type-safe class will be created, and will
+                // be returned by this property.
                 return commandResponse.Value.ToString();
+#nullable enable
             }
         }
 
@@ -312,11 +327,14 @@ public virtual void Click()
             this.Execute(DriverCommand.ClickElement, parameters);
         }
 
+#nullable restore
+
         /// <summary>
         /// Finds the first <see cref="IWebElement"/> using the given method.
         /// </summary>
         /// <param name="by">The locating mechanism to use.</param>
         /// <returns>The first matching <see cref="IWebElement"/> on the current context.</returns>
+        /// <exception cref="ArgumentNullException">If <paramref name="by"/> is <see langword="null"/>.</exception>
         /// <exception cref="NoSuchElementException">If no element matches the criteria.</exception>
         public virtual IWebElement FindElement(By by)
         {
@@ -328,6 +346,8 @@ public virtual IWebElement FindElement(By by)
             return by.FindElement(this);
         }
 
+#nullable enable
+
         /// <summary>
         /// Finds a child element matching the given mechanism and value.
         /// </summary>
@@ -346,6 +366,8 @@ public virtual IWebElement FindElement(string mechanism, string value)
             return this.driver.GetElementFromResponse(commandResponse);
         }
 
+#nullable restore
+
         /// <summary>
         /// Finds all <see cref="IWebElement">IWebElements</see> within the current context
         /// using the given mechanism.
@@ -363,6 +385,8 @@ public virtual ReadOnlyCollection<IWebElement> FindElements(By by)
             return by.FindElements(this);
         }
 
+#nullable enable
+
         /// <summary>
         /// Finds all child elements matching the given mechanism and value.
         /// </summary>
@@ -418,15 +442,14 @@ public virtual ReadOnlyCollection<IWebElement> FindElements(string mechanism, st
         /// via JavaScript.
         /// </remarks>
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
-        public virtual string GetAttribute(string attributeName)
+        public virtual string? GetAttribute(string attributeName)
         {
-            Response commandResponse = null;
-            string attributeValue = string.Empty;
             Dictionary<string, object> parameters = new Dictionary<string, object>();
             string atom = GetAtom("get-attribute.js");
             parameters.Add("script", atom);
             parameters.Add("args", new object[] { ((IWebDriverObjectReference)this).ToDictionary(), attributeName });
-            commandResponse = this.Execute(DriverCommand.ExecuteScript, parameters);
+
+            Response commandResponse = Execute(DriverCommand.ExecuteScript, parameters);
 
 
             // Normalize string values of boolean results as lowercase.
@@ -451,7 +474,7 @@ public virtual string GetAttribute(string attributeName)
         /// of an IDL property of the element, either use the <see cref="GetAttribute(string)"/>
         /// method or the <see cref="GetDomProperty(string)"/> method.
         /// </remarks>
-        public virtual string GetDomAttribute(string attributeName)
+        public virtual string? GetDomAttribute(string attributeName)
         {
             Dictionary<string, object> parameters = new Dictionary<string, object>();
             parameters.Add("id", this.Id);
@@ -469,7 +492,7 @@ public virtual string GetDomAttribute(string attributeName)
         /// <returns>The JavaScript property's current value. Returns a <see langword="null"/> if the
         /// value is not set or the property does not exist.</returns>
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
-        public virtual string GetDomProperty(string propertyName)
+        public virtual string? GetDomProperty(string propertyName)
         {
             Dictionary<string, object> parameters = new Dictionary<string, object>();
             parameters.Add("id", this.Id);
@@ -492,12 +515,12 @@ public virtual ISearchContext GetShadowRoot()
             parameters.Add("id", this.Id);
 
             Response commandResponse = this.Execute(DriverCommand.GetElementShadowRoot, parameters);
-            if (commandResponse.Value is not Dictionary<string, object> shadowRootDictionary)
+            if (commandResponse.Value is not Dictionary<string, object?> shadowRootDictionary)
             {
                 throw new WebDriverException("Get shadow root command succeeded, but response value does not represent a shadow root.");
             }
 
-            if (!ShadowRoot.TryCreate(this.driver, shadowRootDictionary, out ShadowRoot shadowRoot))
+            if (!ShadowRoot.TryCreate(this.driver, shadowRootDictionary, out ShadowRoot? shadowRoot))
             {
                 throw new WebDriverException("Get shadow root command succeeded, but response value does not have a shadow root key value.");
             }
@@ -523,7 +546,9 @@ public virtual string GetCssValue(string propertyName)
             parameters.Add("name", propertyName);
 
             Response commandResponse = this.Execute(DriverCommand.GetElementValueOfCssProperty, parameters);
-            return commandResponse.Value.ToString();
+
+            commandResponse.EnsureValueIsNotNull();
+            return commandResponse.Value.ToString()!;
         }
 
         /// <summary>
@@ -537,7 +562,9 @@ public virtual Screenshot GetScreenshot()
 
             // Get the screenshot as base64.
             Response screenshotResponse = this.Execute(DriverCommand.ElementScreenshot, parameters);
-            string base64 = screenshotResponse.Value.ToString();
+
+            screenshotResponse.EnsureValueIsNotNull();
+            string base64 = screenshotResponse.Value.ToString()!;
 
             // ... and convert it.
             return new Screenshot(base64);
@@ -595,7 +622,7 @@ public virtual void SendKeys(string text)
         /// <exception cref="StaleElementReferenceException">Thrown when the target element is no longer valid in the document DOM.</exception>
         public virtual void Submit()
         {
-            string elementType = this.GetAttribute("type");
+            string? elementType = this.GetAttribute("type");
             if (elementType != null && elementType == "submit")
             {
                 this.Click();
@@ -639,7 +666,7 @@ public override int GetHashCode()
         /// </summary>
         /// <param name="obj">Object to compare against</param>
         /// <returns>A boolean if it is equal or not</returns>
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             if (obj is not IWebElement other)
             {
@@ -674,6 +701,8 @@ Dictionary<string, object> IWebDriverObjectReference.ToDictionary()
             return elementDictionary;
         }
 
+#nullable restore
+
         /// <summary>
         /// Executes a command on this element using the specified parameters.
         /// </summary>
@@ -685,6 +714,8 @@ protected virtual Response Execute(string commandToExecute, Dictionary<string, o
             return this.driver.InternalExecute(commandToExecute, parameters);
         }
 
+#nullable enable
+
         private static string GetAtom(string atomResourceName)
         {
             string atom = string.Empty;
@@ -719,7 +750,9 @@ private string UploadFile(string localFile)
                 Dictionary<string, object> parameters = new Dictionary<string, object>();
                 parameters.Add("file", base64zip);
                 Response response = this.Execute(DriverCommand.UploadFile, parameters);
-                return response.Value.ToString();
+
+                response.EnsureValueIsNotNull();
+                return response.Value.ToString()!;
             }
             catch (IOException e)
             {