fix empty array following the coding style .

Signed-off-by: furplag <furplag@furplag.jp>

lib/Service/NegativeSampleGenerator.php

@@ -71,7 +71,7 @@ private function getUniqueIPsPerUser(Dataset $positives): array {
 	private function generateFromRealData(array $uidVec, array $uniqueIps): array {
 		return array_merge(
 			$uidVec,
-			empty($uniqueIps) ? array() : $uniqueIps[random_int(0, count($uniqueIps) - 1)]
+			empty($uniqueIps) ? [] : $uniqueIps[random_int(0, count($uniqueIps) - 1)]
 		);
 	}