git/githistory/log: handle tasks with no output

git/githistory/log/log.go

@@ -203,7 +203,12 @@ func (l *Logger) logTask(task Task) {
 		}
 	}
 
-	l.log(fmt.Sprintf("%s, done\n", update.S))
+	if update != nil {
+		// If a task sent no updates, the last recorded update will be
+		// nil. Given this, only log a message when there was at least
+		// (1) update.
+		l.log(fmt.Sprintf("%s, done\n", update.S))
+	}
 }
 
 // logLine writes a complete line and moves the cursor to the beginning of the

git/githistory/log/log_test.go

@@ -175,3 +175,16 @@ func TestLoggerLogsAllDurableUpdates(t *testing.T) {
 		"second, done\n",
 	}, ""), buf.String())
 }
+
+func TestLoggerHandlesSilentTasks(t *testing.T) {
+	var buf bytes.Buffer
+
+	task := make(chan *Update)
+	close(task)
+
+	l := NewLogger(&buf)
+	l.Enqueue(ChanTask(task))
+	l.Close()
+
+	assert.Equal(t, "", buf.String())
+}