If LevelFieldName is empty don't log level (#313)

log.go

@@ -424,7 +424,7 @@ func (l *Logger) newEvent(level Level, done func(string)) *Event {
 	e := newEvent(l.w, level)
 	e.done = done
 	e.ch = l.hooks
-	if level != NoLevel {
+	if level != NoLevel && LevelFieldName != "" {
 		e.Str(LevelFieldName, LevelFieldMarshalFunc(level))
 	}
 	if l.context != nil && len(l.context) > 1 {

log_test.go

@@ -77,6 +77,24 @@ func TestInfo(t *testing.T) {
 	})
 }
 
+func TestEmptyLevelFieldName(t *testing.T) {
+	fieldName := LevelFieldName
+	LevelFieldName = ""
+
+	t.Run("empty setting", func(t *testing.T) {
+		out := &bytes.Buffer{}
+		log := New(out)
+		log.Info().
+			Str("foo", "bar").
+			Int("n", 123).
+			Msg("")
+		if got, want := decodeIfBinaryToString(out.Bytes()), `{"foo":"bar","n":123}`+"\n"; got != want {
+			t.Errorf("invalid log output:\ngot:  %v\nwant: %v", got, want)
+		}
+	})
+	LevelFieldName = fieldName
+}
+
 func TestWith(t *testing.T) {
 	out := &bytes.Buffer{}
 	ctx := New(out).With().