Improve log message when no CSRF token found

Closes gh-10436

web/src/main/java/org/springframework/security/web/csrf/MissingCsrfTokenException.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2013 the original author or authors.
+ * Copyright 2002-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,6 @@ package org.springframework.security.web.csrf;
 public class MissingCsrfTokenException extends CsrfException {
 
 	public MissingCsrfTokenException(String actualToken) {
-		super("Could not verify the provided CSRF token because your session was not found.");
+		super("Could not verify the provided CSRF token because no token was found to compare.");
 	}
 }