Mark $_SESSION as nullable

Author: b1rdex

src/Rules/Variables/VariableCertaintyInIssetRule.php

@@ -39,7 +39,7 @@ public function processNode(Node $node, Scope $scope): array
 				$isSubNode = true;
 			}
 
-			if (!$var instanceof Node\Expr\Variable || !is_string($var->name)) {
+			if (!$var instanceof Node\Expr\Variable || !is_string($var->name) || $var->name === '_SESSION') {
 				continue;
 			}
 

tests/PHPStan/Rules/Variables/data/variable-certainty-isset.php

@@ -226,3 +226,8 @@ function () {
 
     }
 };
+
+function () {
+    isset($_SESSION);
+    isset($_SESSION['foo']);
+};