Do not expect metadata until expecting first read
diff --git a/src/php/lib/Grpc/AbstractCall.php b/src/php/lib/Grpc/AbstractCall.php
index d81df97..413d596 100644
--- a/src/php/lib/Grpc/AbstractCall.php
+++ b/src/php/lib/Grpc/AbstractCall.php
@@ -47,6 +47,7 @@
   public function __construct(Channel $channel, $method, $deserialize) {
     $this->call = new Call($channel, $method, Timeval::inf_future());
     $this->deserialize = $deserialize;
+    $this->metadata = null;
   }
 
   /**