Butler: fix global tags applied to empty map.

logdog/client/butler/butler.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package butler
 
 import (
         "errors"
         "fmt"
         "io"
@@ skipping 388 matching lines @@
         p = p.Clone()
         if p.Timestamp == nil || p.Timestamp.Time().IsZero() {
                 p.Timestamp = google.NewTimestamp(clock.Now(b.ctx))
         }
         if err := p.Validate(); err != nil {
                 return err
         }
 
         // Build per-stream tag map.
         if l := len(b.c.GlobalTags); l > 0 {
+                if p.Tags == nil {
+                        p.Tags = make(map[string]string, l)
+                }
+
                 for k, v := range b.c.GlobalTags {
                         // Add only global flags that aren't already present (overridden) in
                         // stream tags.
                         if _, ok := p.Tags[k]; !ok {
                                 p.Tags[k] = v
                         }
                 }
         }
 
         if p.Timeout > 0 {
@@ skipping 239 matching lines @@
         // shutdown prematurely, so this should be reasonably quick.
         b.Activate()
 }
 
 // Returns the configured Butler error.
 func (b *Butler) getRunErr() error {
         b.shutdownMu.Lock()
         defer b.shutdownMu.Unlock()
         return b.runErr
 }