CSS Validator Incorrectly Finds Errors with Nested Pseudo-Class

The validator at https://jigsaw.w3.org/css-validator/#validate_by_input finds errors (incorrectly) with nested pseudo-class selectors. 
It found the following error for an example from the standard.  6     .foo     Parse Error &:hover { color: blue; } The example of proper nesting is from https://www.w3.org/TR/css-nesting-1/.foo {
  color: red;

  &:hover {"
    color: blue;
  }
}

I discovered the problem trying to validate nested use of ":empty".
Regards,John Joyce