Update Expression_language: lint function

The lint function doesn't return anything but exception.

Second arguments with Flags example is ommitted.

Author: kl3sk

components/expression_language.rst

@@ -103,7 +103,9 @@ other hand, returns a boolean indicating if the expression is valid or not::
     // displays the AST nodes of the expression which can be
     // inspected and manipulated
 
-    var_dump($expressionLanguage->lint('1 + 2', [])); // displays true
+    $expressionLanguage->lint('1 + a', []);
+    // Throw SyntaxError Exception
+    // "Variable "a" is not valid around position 5 for expression `1 + a`."
 
 The behavior of these methods can be configured with some flags defined in the
 :class:`Symfony\\Component\\ExpressionLanguage\\Parser` class:
@@ -120,8 +122,8 @@ This is how you can use these flags::
 
     $expressionLanguage = new ExpressionLanguage();
 
-    // this returns true because the unknown variables and functions are ignored
-    var_dump($expressionLanguage->lint('unknown_var + unknown_function()', Parser::IGNORE_UNKNOWN_VARIABLES | Parser::IGNORE_UNKNOWN_FUNCTIONS));
+    // this returns null because the unknown variables and functions are ignored, but don't throw `SyntaxError` exception
+    var_dump($expressionLanguage->lint('unknown_var + unknown_function()', [], Parser::IGNORE_UNKNOWN_VARIABLES | Parser::IGNORE_UNKNOWN_FUNCTIONS));
 
 .. versionadded:: 7.1