handle null sql iso8601, kitchen time and simple date column values

x/jsonx/iso8601.go

@@ -104,6 +104,8 @@ func (t *ISO8601) Scan(src interface{}) error {
 			return err
 		}
 		*t = tt
+	case nil:
+		*t = ISO8601(time.Time{})
 	default:
 		return fmt.Errorf("ISO8601: unknown type of: %T", v)
 	}

x/jsonx/kitchen_time.go

@@ -100,6 +100,8 @@ func (t *KitckenTime) Scan(src interface{}) error {
 			return err
 		}
 		*t = tt
+	case nil:
+		*t = KitckenTime(time.Time{})
 	default:
 		return fmt.Errorf("KitckenTime: unknown type of: %T", v)
 	}

x/jsonx/simple_date.go

@@ -105,6 +105,8 @@ func (t *SimpleDate) Scan(src interface{}) error {
 			return err
 		}
 		*t = tt
+	case nil:
+		*t = SimpleDate(time.Time{})
 	default:
 		return fmt.Errorf("SimpleDate: unknown type of: %T", v)
 	}