fix typing of nullable parameters

Author: shu-yusa

composer.json

@@ -7,7 +7,8 @@
   "license": "Apache-2.0",
   "version": "1.57.0",
   "require": {
-    "php": ">=7.0.0"
+    "php": ">=7.1.0",
+    "ext-grpc": "*"
   },
   "suggest": {
     "ext-protobuf": "For better performance, install the protobuf C extension.",

src/lib/ServerCallWriter.php

@@ -81,7 +81,7 @@ public function finish(
 
     private function addSendInitialMetadataOpIfNotSent(
         array &$batch,
-        array $initialMetadata = null
+        ?array $initialMetadata = null
     ) {
         if (!$this->initialMetadataSent_) {
             $batch[OP_SEND_INITIAL_METADATA] = $initialMetadata ?? [];

src/lib/Status.php

@@ -32,7 +32,7 @@
  */
 class Status
 {
-    public static function status(int $code, string $details, array $metadata = null): array
+    public static function status(int $code, string $details, ?array $metadata = null): array
     {
         $status = [
             'code' => $code,
@@ -44,7 +44,7 @@ public static function status(int $code, string $details, array $metadata = null
         return $status;
     }
 
-    public static function ok(array $metadata = null): array
+    public static function ok(?array $metadata = null): array
     {
         return Status::status(STATUS_OK, 'OK', $metadata);
     }