PHP Notice: "Undefined offset: 2" if allowed_hosts contains subdomains

[codegain]

Hi,

I recently got the following error:

Notice: Undefined offset: 2

here:

html-sanitizer/src/Sanitizer/UrlSanitizerTrait.php

Line 83 in d2dd64c

if ($uriParts[$key] !== $trustedPart) {

I got this error after adding a subdomain to allowed_hosts like sub.example.org and this causes the function to be called with the following parameters if a url like https://example.org in a href attribute is sanitized:

$uriParts = ['org', 'example']; 
$trustedParts = ['org', 'example', 'sub'];

Is a subdomain not allowed in allowed_hosts or is this a bug?