Variables don't have a class, so we can't use toString() on it

lib/private/app/codechecker/nodevisitor.php

@@ -167,11 +167,11 @@ class NodeVisitor extends NodeVisitorAbstract {
 					 *       $c = "OC_API";
 					 *       $n = $i::ADMIN_AUTH;
 					 */
-				}
-
+				} else {
 					$this->checkBlackListConstant($node->class->toString(), $node->name, $node);
 				}
 			}
+		}
 		if ($node instanceof Node\Expr\New_) {
 			if (!is_null($node->class)) {
 				if ($node->class instanceof Name) {