Hello,
if I activate WP_DEBUG_LOG in wp-config.php, almost instantly the file debug.log is filled with multiple lines, for example:

[19-Feb-2017 16:41:52 UTC] Array
(
    [akismet_debug] => Array
        (
            [akismet_url] => https://NUMERIC_STRING.rest.akismet.com/1.1/verify-key
            [http_args] => Array
                (
                    [body] => key=NUMERIC_STRING&blog=https%3A%2F%2Fwww.example.com
                    [headers] => Array
                        (
                            [Content-Type] => application/x-www-form-urlencoded; charset=UTF-8
                            [Host] => NUMERIC_STRING.rest.akismet.com
                            [User-Agent] => WordPress/4.7.2 | Akismet/3.2
                        )

                    [httpversion] => 1.0
                    [timeout] => 15
                )

            [response] => Array

and so on. In the original file there is a numeric string instead of NUMERIC_STRING.

I’m using WP 4.7.2, Akismet 3.2, Apache, PHP 5.6.30.

Why I receive such notices?

Thanks in advance.