Steps to reproduce:
1. Create custom filed (Maniphest) with type user
2. Create herald rule (Maniphest task) on this filed with "include any of"
3. Try to create task
```
COUNTEREXAMPLE
Argument 1 passed to array_fuse() must be of the type array, null given, called in /phabricator/src/applications/herald/adapter/HeraldAdapter.php on line 382 and defined
```
I think this also "works" with other PHID based fields and other applications.
Simplest resolution is to overide method getFieldVlaue in PhabricatorStandardCustomFieldPHIDS to return array if parent return null.
```
lang=php
public function getFieldValue()
{
$value = parent::getFieldValue();
if ($value) {
return $value;
}
return array();
}
```