Make sure node map is valid before accessing it

Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>

libnetwork/networkdb/delegate.go

@@ -2,6 +2,7 @@ package networkdb
 
 import (
 	"fmt"
+	"net"
 	"time"
 
 	"github.com/Sirupsen/logrus"
@@ -210,8 +211,13 @@ func (nDB *NetworkDB) handleBulkSync(buf []byte) {
 		return
 	}
 
+	var nodeAddr net.IP
+	if node, ok := nDB.nodes[bsm.NodeName]; ok {
+		nodeAddr = node.Addr
+	}
+
 	if err := nDB.bulkSyncNode(bsm.Networks, bsm.NodeName, false); err != nil {
-		logrus.Errorf("Error in responding to bulk sync from node %s: %v", nDB.nodes[bsm.NodeName].Addr, err)
+		logrus.Errorf("Error in responding to bulk sync from node %s: %v", nodeAddr, err)
 	}
 }