Update packages/realtime_client/lib/src/realtime_channel.dart

Co-authored-by: Bruno D'Luka <45696119+bdlukaa@users.noreply.github.com>

Author: dshukertjr

packages/realtime_client/lib/src/realtime_channel.dart

@@ -491,7 +491,8 @@ class RealtimeChannel {
     if (!canPush && type == RealtimeListenTypes.broadcast) {
       final headers = <String, String>{
         'Content-Type': 'application/json',
-        'apikey': socket.params['apikey'] ?? '',
+        if (socket.params['apikey'] != null)
+          'apikey': socket.params['apikey']!,
         ...socket.headers,
         'Authorization':
             socket.accessToken != null ? 'Bearer ${socket.accessToken}' : '',