Make null logger a pointer type (#108)

log/logger.go

@@ -125,12 +125,10 @@ func (f Fields) ValueAt(i int) Field { return f[i] }
 // NullLogger is a logger that emits nowhere.
 var NullLogger Logger = nullLogger{}
 
-type nullLogger struct {
-	fields Fields
-}
+type nullLogger struct{}
 
 func (nullLogger) Enabled(_ Level) bool                   { return false }
-func (nullLogger) Fatalf(msg string, args ...interface{}) {}
+func (nullLogger) Fatalf(msg string, args ...interface{}) { os.Exit(1) }
 func (nullLogger) Fatal(msg string)                       { os.Exit(1) }
 func (nullLogger) Errorf(msg string, args ...interface{}) {}
 func (nullLogger) Error(msg string)                       {}
@@ -140,23 +138,8 @@ func (nullLogger) Infof(msg string, args ...interface{})  {}
 func (nullLogger) Info(msg string)                        {}
 func (nullLogger) Debugf(msg string, args ...interface{}) {}
 func (nullLogger) Debug(msg string)                       {}
-func (l nullLogger) Fields() LoggerFields                 { return l.fields }
-
-func (l nullLogger) WithFields(newFields ...Field) Logger {
-	existingLen := 0
-
-	existingFields := l.Fields()
-	if existingFields != nil {
-		existingLen = existingFields.Len()
-	}
-
-	fields := make([]Field, 0, existingLen+len(newFields))
-	for i := 0; i < existingLen; i++ {
-		fields = append(fields, existingFields.ValueAt(i))
-	}
-	fields = append(fields, newFields...)
-	return nullLogger{Fields(fields)}
-}
+func (l nullLogger) Fields() LoggerFields                 { return nil }
+func (l nullLogger) WithFields(...Field) Logger           { return l }
 
 // SimpleLogger prints logging information to standard out.
 var SimpleLogger = NewLogger(os.Stdout)