Add this filter to the query.
Due to the nature of fapi, the value and the operator have an unintended level of indirection. You will find them in $this->operator and $this->value respectively.
Overrides FilterPluginBase::query
public function query() {
$this
->ensureMyTable();
$field = "{$this->tableAlias}.{$this->realField}";
$info = $this
->operators();
if (!empty($info[$this->operator]['method'])) {
$this
->{$info[$this->operator]['method']}($field);
}
}