message: Use Object.create(null) for Viewer properties.
diff: @@ -88,7 +88,7 @@ class PdfViewerPanelSerializer implements vscode.WebviewPanelSerializer {
  export class Viewer {
  private readonly extension: Extension
  private readonly webviewPanels = new Map<string, Set<PdfViewerPanel>>()
  - readonly clients: {[key: string]: Set<Client>} = {}
  + readonly clients = Object.create(null) as { [key: string]: Set<Client> }
  readonly pdfViewerPanelSerializer: PdfViewerPanelSerializer
  constructor(extension: Extension) {
  