This was working in 2.2.x
$query = \CouchbaseN1qlQuery::fromString("SELECT * FROM system:indexes WHERE name='{$name}' AND keyspace_id='{$this->name}'", NULL, FALSE);
It is now returning NULL in 2.3.x. Seems like old extension implementation was taking additional arguments, this change should be described in a changelog or something… removing NULL and FALSE from parameter list fixes it, but still the behaviour (returning null) is really strange…