UnmarshalJSON in Int now returns an error message when asked to unmarshal from an invalid type. This is in line with the behavior of the built-in sql.NullInt64.

bool.go

@@ -4,6 +4,7 @@ import (
 	"database/sql"
 	"encoding/json"
 	"errors"
+	// "fmt"
 )
 
 // Bool is an even nuller nullable bool.
@@ -52,6 +53,8 @@ func (b *Bool) UnmarshalJSON(data []byte) error {
 	case nil:
 		b.Valid = false
 		return nil
+		// default:
+		// 	err = fmt.Errorf("json: cannot unmarshal %v into Go value of type null.Bool", v.(type).Name())
 	}
 	b.Valid = err == nil
 	return err

int.go

@@ -3,6 +3,8 @@ package null
 import (
 	"database/sql"
 	"encoding/json"
+	"fmt"
+	"reflect"
 	"strconv"
 )
 
@@ -52,6 +54,8 @@ func (i *Int) UnmarshalJSON(data []byte) error {
 	case nil:
 		i.Valid = false
 		return nil
+	default:
+		err = fmt.Errorf("json: cannot unmarshal %v into Go value of type null.Int", reflect.TypeOf(v).Name())
 	}
 	i.Valid = err == nil
 	return err