Found ':' but no key name (for an empty key name use quotes)

[luizbills]

{
  0: 0
}

When I try parse the code above, I receive this error: Found ':' but no key name (for an empty key name use quotes) at line 2, 4 >>> 0: 0 } .... But this hjson code works in https://hjson.org/try.html

my code:

$hjson_parser = new HJSONParser();
try {
  $variables = $hjson_parser->parse( $hjson_text );
} catch ( Exception $e ) {
  ...
}