do not do log.Errorln when checkpoint is not found (which is normal)

go/cmd/pserver/pserver.go

@@ -59,9 +59,13 @@ func main() {
 
 		cp, err = pserver.NewCheckpointFromFile(*checkpointPath, idx, e)
 		if err != nil {
+			if err == pserver.ErrCheckpointNotFound {
+				log.Infof("Could not find the pserver checkpoint.")
+			} else {
 				log.Errorf("Fetch checkpoint failed, %s", err)
 			}
 		}
+	}
 
 	s, err := pserver.NewService(idx, *checkpointInterval, *checkpointPath, e, cp)
 	candy.Must(err)

go/pserver/service.go

@@ -36,6 +36,10 @@ import (
 // ElementType is the type of elements of a Parameter.
 type ElementType int
 
+// ErrCheckpointNotFound indicates that the pserver checkpoint could
+// not be found.
+var ErrCheckpointNotFound = errors.New("checkpoint not found")
+
 // RPC error message.
 const (
 	AlreadyInitialized  = "pserver already initialized"
@@ -103,6 +107,10 @@ func NewCheckpointFromFile(cpPath string, idx int, e *EtcdClient) (Checkpoint, e
 		return nil, err
 	}
 
+	if len(v) == 0 {
+		return nil, ErrCheckpointNotFound
+	}
+
 	var cpMeta checkpointMeta
 	if err = json.Unmarshal(v, &cpMeta); err != nil {
 		return nil, err