Merge pull request #1439 from hmiyado/fix-timestamp-getvalue

Fix timestamp flag error when using help

--

I'm merging this with the codecov patch check failing because this fixes a bug in code that wasn't sufficiently covered prior to the fix. In other words, I don't consider this codecov failure to be specific to this PR.

flag_timestamp.go

@@ -90,7 +90,7 @@ func (f *TimestampFlag) GetCategory() string {
 // GetValue returns the flags value as string representation and an empty
 // string if the flag takes no value at all.
 func (f *TimestampFlag) GetValue() string {
-	if f.Value != nil {
+	if f.Value != nil && f.Value.timestamp != nil {
 		return f.Value.timestamp.String()
 	}
 	return ""