Unable to remove a date from index

[lozcalver]

Given an index which includes a date (haven’t tested addFulltextField instead of addFilterField, but I suspect it’s the same):

<?php

namespace App\Indexes;

use App\Model\Documents\Document;
use Firesphere\SolrSearch\Indexes\BaseIndex;

class DocumentIndex extends BaseIndex
{
    public function init()
    {
        $this->addClass(Document::class);
        $this->addFulltextField('Title');
        $this->addFulltextField('FileContent');
        $this->addFilterField('Embargo'); // Date
        $this->addFilterField('Expiry'); // Date
    }

    public function getIndexName()
    {
        return 'document';
    }
}

If you set a date against an object, it’s added to the index as expected. If you then remove that date (it’s set to NULL in the database), it’s not removed from the index.

DocumentFactory seems to explicitly filter out null values here:

silverstripe-solr-search/src/Factories/DocumentFactory.php

Lines 177 to 179 in 52398a4

	if ($value === null) {
	continue;
	}

I’m not sure if there’s any reason why?