fields map reference issue

fields.go

@@ -2,9 +2,14 @@ package log
 
 func (l myLogger) WithFields(fields Fields) Logger {
 	if l.data != nil && len(l.data) > 0 {
-		for k, v := range fields {
-			l.data[k] = v
+		f := Fields{}
+		for k, v := range l.data {
+			f[k] = v
 		}
+		for k, v := range fields {
+			f[k] = v
+		}
+		l.data = f
 	} else {
 		l.data = fields
 	}