strlen() was used in Phabricator to check if a generic value is a non-empty string.
This behavior is deprecated since PHP 8.1. Phorge adopts phutil_nonempty_string() as a replacement.

Note: this may highlight other absurd input values that might be worth correcting
instead of just ignoring. If phutil_nonempty_string() throws an exception in your
instance, report it to Phorge to evaluate and fix that specific corner case.

Closes T15312

Applied this change (on top of D25144, D25145, D25146, D25147, D25151, D25152, D25153 and /project/query/active/ rendered correctly in web browser.

Tested surfing various pages with and without Maniphest's maniphest.subtypes.

If you need some example custom fields, this is an example:

[
    {
      "key": "default",
      "name": "Task"
    },
    {
      "key": "bug",
      "name": "Bug"
    },
    {
      "key": "log",
      "name": "LogSpam"
    },
    {
      "key": "deadline",
      "name": "Deadline"
    }
  ]