Omit zero time.Time default from usage line

This was missed in #348, there previously was no way to omit the
default value. Treating zero timestamp values as canary for absence
of a default is in line with other flag types, e.g. zero ints.

1 files changed, 7 insertions, 1 deletions

diff --git a/time.go b/time.go
index dc02480..3dee424 100644
--- a/time.go
+++ b/time.go
@@ -48,7 +48,13 @@ func (d *timeValue) Type() string {
 	return "time"
 }
 
-func (d *timeValue) String() string { return d.Time.Format(time.RFC3339Nano) }
+func (d *timeValue) String() string {
+	if d.Time.IsZero() {
+		return ""
+	} else {
+		return d.Time.Format(time.RFC3339Nano)
+	}
+}
 
 // GetTime return the time value of a flag with the given name
 func (f *FlagSet) GetTime(name string) (time.Time, error) {