Fix handling of emtpy sink configs

Toml parsing library can return nil in case the object on the list
that is instantiated doesn't have any properties set. This change
fixes that by creating default emtpy object so we don't crash.

pkg/config/config.go

@@ -137,6 +137,9 @@ func parseTLSConfig(config *fTLSConfig, defaultServerName string, basePath strin
 }
 
 func parseMQTTSink(basePath string, sinkID int, sink *fMQTTSink) (*MQTTSink, error) {
+	if sink == nil {
+		sink = &fMQTTSink{}
+	}
 	res := &MQTTSink{}
 	if sink.Name == "" {
 		res.Name = fmt.Sprintf("unnamed-mqtt-sink-%d", sinkID)
@@ -196,6 +199,9 @@ func parseMQTTSink(basePath string, sinkID int, sink *fMQTTSink) (*MQTTSink, err
 }
 
 func parseCloudPubSubSink(basePath string, sinkID int, sink *fCloudPubSubSink) (*CloudPubSubSink, error) {
+	if sink == nil {
+		sink = &fCloudPubSubSink{}
+	}
 	ctx := context.Background()
 	res := &CloudPubSubSink{}
 	if sink.Name == "" {
@@ -246,6 +252,9 @@ func parseCloudPubSubSink(basePath string, sinkID int, sink *fCloudPubSubSink) (
 }
 
 func parseStdoutSink(sinkID int, sink *fStdoutSink) (*StdoutSink, error) {
+	if sink == nil {
+		sink = &fStdoutSink{}
+	}
 	res := &StdoutSink{}
 	if sink.Name == "" {
 		res.Name = fmt.Sprintf("unnamed-stdout-sink-%d", sinkID)

pkg/config/config_test.go

@@ -134,3 +134,21 @@ func TestParsingEmpty(t *testing.T) {
 		t.Errorf("unexpected difference:\n%v", diff)
 	}
 }
+
+func TestParsingEmptySink(t *testing.T) {
+	config, err := Read("testdata/test2/config.toml")
+	if err != nil {
+		t.Fatalf("Failed to parse config: %v", err)
+	}
+	expectedConfig := &Config{
+		Adapter: "hci0",
+		Sinks: []Sink{
+			&StdoutSink{
+				Name: "unnamed-stdout-sink-0",
+			},
+		},
+	}
+	if diff := cmpConfig(config, expectedConfig); diff != "" {
+		t.Errorf("unexpected difference:\n%v", diff)
+	}
+}

pkg/config/testdata/test2/config.toml

@@ -0,0 +1 @@
+[[sinks.stdout]]