wp_check_filetype() returns false for html files

[onnimonni]

Is this intentional behaviour?

Running:

<?php
var_dump( wp_check_filetype( 'example.html' ) );

outputs:

array(2) {
  'ext' =>
  bool(false)
  'type' =>
  bool(false)
}

WordPress and PHP versions:

$ wp core version
4.7.1
$ php --version
PHP 7.0.15-1~dotdeb+8.1 (cli) ( NTS )
Copyright (c) 1997-2017 The PHP Group
Zend Engine v3.0.0, Copyright (c) 1998-2017 Zend Technologies
    with Zend OPcache v7.0.15-1~dotdeb+8.1, Copyright (c) 1999-2017, by Zend Technologies
    with Xdebug v2.5.0, Copyright (c) 2002-2016, by Derick Rethans

Hi @onnimonni. This is probably related to #39550.