Symfony version(s) affected: 3.4.27
I reproduce symfony/yaml@e464640

Description
Comments after blank lines are read as value in yaml.

How to reproduce

$yaml = <<<YAML
parameters:
    abc

# Comment 
YAML;

var_dump(Symfony\Component\Yaml\Yaml::parse($yaml));

Actual result:

array(1) {
  ["parameters"]=>
  string(13) "abc
# Comment"
}

Expected result:

array(1) {
  ["parameters"]=>
  string(3) "abc"
}

Possible Solution
Ignore comment line.

Additional context
When I tested some Online YAML parser, I got the expected results.
https://yaml-online-parser.appspot.com/?yaml=parameters%3A%0A++++abc%0A%0A%23+Comment%0A&type=json
http://nodeca.github.io/js-yaml/#yaml=cGFyYW1ldGVyczoKICAgIGFiYwoKIyBDb21tZW50IAo=