database/sql: add NullTime

This matches NullBool, NullFloat64, and NullInt64.

Fixes #30305

Change-Id: I79bfcf04a3d43b965d2a3159b0ac22f3e8084a53
Reviewed-on: https://go-review.googlesource.com/c/go/+/170699
Run-TryBot: Daniel Theophanes <kardianos@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/sql.go

@@ -286,6 +286,32 @@ func (n NullBool) Value() (driver.Value, error) {
 	return n.Bool, nil
 }
 
+// NullTime represents a time.Time that may be null.
+// NullTime implements the Scanner interface so
+// it can be used as a scan destination, similar to NullString.
+type NullTime struct {
+	Time  time.Time
+	Valid bool // Valid is true if Time is not NULL
+}
+
+// Scan implements the Scanner interface.
+func (n *NullTime) Scan(value interface{}) error {
+	if value == nil {
+		n.Time, n.Valid = time.Time{}, false
+		return nil
+	}
+	n.Valid = true
+	return convertAssign(&n.Time, value)
+}
+
+// Value implements the driver Valuer interface.
+func (n NullTime) Value() (driver.Value, error) {
+	if !n.Valid {
+		return nil, nil
+	}
+	return n.Time, nil
+}
+
 // Scanner is an interface used by Scan.
 type Scanner interface {
 	// Scan assigns a value from a database driver.