don't assume a server agent necesarily exists (#286)

Author: transistive

src/BoltFactory.php

@@ -78,7 +78,7 @@ public function createConnection(ConnectionRequestData $data, SessionConfigurati
 
         $response = $data->getAuth()->authenticateBolt($connection, $data->getUserAgent());
 
-        $config->setServerAgent($response['server']);
+        $config->setServerAgent($response['server'] ?? '');
 
         return $connection;
     }

tests/Unit/BoltFactoryTest.php

@@ -107,4 +107,34 @@ public function testBoltFactoryWithSocketTypeOverride(): void
         $factory = BoltFactory::create(null, SocketType::STREAM());
         self::assertInstanceOf(BoltFactory::class, $factory);
     }
+
+    public function testCreateConnectionWithNullServerAgent(): void
+    {
+        // This test reproduces issue #285 where authenticateBolt returns null for server
+        $auth = $this->createMock(AuthenticateInterface::class);
+        $auth->method('authenticateBolt')
+            ->willReturn(['server' => null, 'connection_id' => 'i', 'hints' => []]);
+
+        $connection = $this->factory->createConnection(
+            new ConnectionRequestData('', Uri::create(''), $auth, '', SslConfiguration::default()),
+            SessionConfiguration::default()
+        );
+
+        self::assertInstanceOf(BoltConnection::class, $connection);
+    }
+
+    public function testCreateConnectionWithMissingServerKey(): void
+    {
+        // This test reproduces issue #285 where authenticateBolt returns response without server key
+        $auth = $this->createMock(AuthenticateInterface::class);
+        $auth->method('authenticateBolt')
+            ->willReturn(['connection_id' => 'i', 'hints' => []]);
+
+        $connection = $this->factory->createConnection(
+            new ConnectionRequestData('', Uri::create(''), $auth, '', SslConfiguration::default()),
+            SessionConfiguration::default()
+        );
+
+        self::assertInstanceOf(BoltConnection::class, $connection);
+    }
 }