fix EligibleAt null / NewNullTime (#471)

* fix EligibleAt null / NewNullTime

* test

database/types.go

@@ -23,10 +23,12 @@ func NewNullString(s string) sql.NullString {
 	}
 }
 
+// NewNullTime returns a sql.NullTime with the given time.Time. If the time is
+// the zero value, the NullTime is invalid.
 func NewNullTime(t time.Time) sql.NullTime {
 	return sql.NullTime{
 		Time:  t,
-		Valid: true,
+		Valid: t != time.Time{},
 	}
 }
 

database/types_test.go

@@ -0,0 +1,19 @@
+package database
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewNullTime(t *testing.T) {
+	var t1 time.Time
+	nt1 := NewNullTime(t1)
+	require.False(t, nt1.Valid)
+
+	t1 = time.Now()
+	nt1 = NewNullTime(t1)
+	require.True(t, nt1.Valid)
+	require.Equal(t, t1, nt1.Time)
+}