fix: initialize broker and subscribers

http.go

@@ -238,6 +238,7 @@ func newServer(opts ...server.Option) server.Server {
 	return &httpServer{
 		opts: newOptions(opts...),
 		exit: make(chan chan error),
+		subscribers: make(map[*httpSubscriber][]broker.Subscriber),
 	}
 }
 

options.go

@@ -3,6 +3,7 @@ package http
 import (
 	"context"
 
+	"github.com/micro/go-micro/broker"
 	"github.com/micro/go-micro/codec"
 	"github.com/micro/go-micro/registry"
 	"github.com/micro/go-micro/server"
@@ -19,6 +20,10 @@ func newOptions(opt ...server.Option) server.Options {
 		o(&opts)
 	}
 
+	if opts.Broker == nil {
+		opts.Broker = broker.DefaultBroker
+	}
+
 	if opts.Registry == nil {
 		opts.Registry = registry.DefaultRegistry
 	}