TypeScipt 2.5.2

Sorry, I wasn't able to extract a simplified example:

• git clone https://github.com/Microsoft/vscode-css-languageservice.git
• cd vscode-css-languageservice
• git checkout 73f8707
• npm install
• npm run compile

src/services/cssCompletion.ts(804,47) error TS2358: The left-hand side of an 'instanceof' expression must be of type 'any', an object type or a type parameter.
link to cssCompletion.ts: 804

It's a new error, not reported by a previous version of typescript.
Both nodes.HexColorValue(link) and nodes.Function(link) are classes that extend base class nodes.Node(link). The way I see it, the instanceof test is valid code to test the runtime types of the object.

Adding a brand field _hexColorValue : void; to nodes.HexColorValue fixes the issue, so maybe this is related to #12083.
At the very least the message should be improved, but IMO the error is invalid.