fix NPD

Author: isopov

x/mongo/driver/topology/topology.go

@@ -824,7 +824,10 @@ func equalTopologies(topo1, topo2 description.Topology) bool {
 	}
 
 	for _, server := range topoServers {
-		otherServer := otherServers[server.Addr.String()]
+		otherServer, ok := otherServers[server.Addr.String()]
+		if !ok {
+			return false
+		}
 
 		if !driverutil.EqualServers(*server, *otherServer) {
 			return false

x/mongo/driver/topology/topology_test.go

@@ -1042,6 +1042,31 @@ func BenchmarkSelectServerFromDescription(b *testing.B) {
 	}
 }
 
+func TestEqualTopologies(t *testing.T) {
+	assert.True(t, equalTopologies(
+		description.Topology{
+			Servers: []description.Server{{
+				Addr: "127.0.0.1:27017",
+			}},
+		}, description.Topology{
+			Servers: []description.Server{{
+				Addr: "127.0.0.1:27017",
+			}},
+		},
+	))
+	assert.False(t, equalTopologies(
+		description.Topology{
+			Servers: []description.Server{{
+				Addr: "127.0.0.1:27017",
+			}},
+		}, description.Topology{
+			Servers: []description.Server{{
+				Addr: "127.0.0.2:27017",
+			}},
+		},
+	))
+}
+
 func BenchmarkEqualTopologies(b *testing.B) {
 	servers := make([]description.Server, 100)
 	for i := 0; i < len(servers); i++ {