TS1011: An element access expression should take an argument

I'm getting this error when exporting interface and was hoping to get some insight in why this happens:

// Interfaces.ts
export interface PortDescription {
  tag?: 'CORE' | 'TRANSIT' | 'SRV';
  name?: string;
  comment?: string;
}

Warning thrown: TS1011: An element access expression should take an argument.

The code compiles without error or warnings and imports works fine so maybe it's just Webstorm giving me a hard time.

I've done the Google part but it did not yield any useful answers.