Fix null warnings

Author: RenderMichael

dotnet/src/webdriver/Chromium/ChromiumDriver.cs

@@ -168,7 +168,7 @@ private static ICommandExecutor GenerateDriverServiceCommandExecutor(DriverServi
                 string fullServicePath = finder.GetDriverPath();
                 service.DriverServicePath = Path.GetDirectoryName(fullServicePath);
                 service.DriverServiceExecutableName = Path.GetFileName(fullServicePath);
-                if (finder.TryGetBrowserPath(out string browserPath))
+                if (finder.TryGetBrowserPath(out string? browserPath))
                 {
                     options.BinaryLocation = browserPath;
                     options.BrowserVersion = null;

dotnet/src/webdriver/Firefox/FirefoxDriver.cs

@@ -221,7 +221,7 @@ private static ICommandExecutor GenerateDriverServiceCommandExecutor(DriverServi
                 string fullServicePath = finder.GetDriverPath();
                 service.DriverServicePath = Path.GetDirectoryName(fullServicePath);
                 service.DriverServiceExecutableName = Path.GetFileName(fullServicePath);
-                if (finder.TryGetBrowserPath(out string browserPath))
+                if (finder.TryGetBrowserPath(out string? browserPath))
                 {
                     options.BinaryLocation = browserPath;
                     options.BrowserVersion = null;

dotnet/src/webdriver/Firefox/FirefoxProfile.cs

@@ -160,7 +160,7 @@ public void WriteToDisk()
             this.ProfileDirectory = GenerateProfileDirectoryName();
             if (!string.IsNullOrEmpty(this.sourceProfileDir))
             {
-                FileUtilities.CopyDirectory(this.sourceProfileDir, this.ProfileDirectory);
+                FileUtilities.CopyDirectory(this.sourceProfileDir!, this.ProfileDirectory);
             }
             else
             {