message: Change fileToOpen to a nullable type
diff: @@ -12,7 +12,7 @@ import { toRange2 } from './typeConversion';
  export async function buildEditForResponse(changes: FileOperationResponse[], languageMiddlewareFeature: LanguageMiddlewareFeature, token: vscode.CancellationToken): Promise<boolean> {
  let edit = new vscode.WorkspaceEdit();
  - let fileToOpen: Uri = null;
  + let fileToOpen: Uri | undefined;
  if (!changes || !Array.isArray(changes) || !changes.length) {
  return true;
  @@ -55,7 +55,7 @@ export async function buildEditForResponse(changes: FileOperationResponse[], lan
  // and replaced with a command that can only close the active editor.
  // If files were renamed that weren't the active editor, their tabs will
  // be left open and marked as "deleted" by VS Code
  - return fileToOpen != null
  + return fileToOpen !== undefined
  ? applyEditPromise.then(_ => {
  return vscode.commands.executeCommand("vscode.open", fileToOpen);
  })
  