More clear for Get with nil (#1879)

Resolve #1844

Reviewed-on: https://gitea.com/xorm/xorm/pulls/1879
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-committed-by: Lunny Xiao <xiaolunwen@gmail.com>

integrations/session_get_test.go

@@ -6,11 +6,13 @@ package integrations
 
 import (
 	"database/sql"
+	"errors"
 	"fmt"
 	"strconv"
 	"testing"
 	"time"
 
+	"xorm.io/xorm"
 	"xorm.io/xorm/contexts"
 	"xorm.io/xorm/schemas"
 
@@ -750,3 +752,17 @@ func TestGetViaMapCond(t *testing.T) {
 	assert.NoError(t, err)
 	assert.False(t, has)
 }
+
+func TestGetNil(t *testing.T) {
+	type GetNil struct {
+		Id int64
+	}
+
+	assert.NoError(t, PrepareEngine())
+	assertSync(t, new(GetNil))
+
+	var gn *GetNil
+	has, err := testEngine.Get(gn)
+	assert.True(t, errors.Is(err, xorm.ErrObjectIsNil))
+	assert.False(t, has)
+}

session_get.go

@@ -16,6 +16,10 @@ import (
 	"xorm.io/xorm/schemas"
 )
 
+var (
+	ErrObjectIsNil = errors.New("object should not be nil")
+)
+
 // Get retrieve one record from database, bean's non-empty fields
 // will be as conditions
 func (session *Session) Get(bean interface{}) (bool, error) {
@@ -37,6 +41,8 @@ func (session *Session) get(bean interface{}) (bool, error) {
 		return false, errors.New("needs a pointer to a value")
 	} else if beanValue.Elem().Kind() == reflect.Ptr {
 		return false, errors.New("a pointer to a pointer is not allowed")
+	} else if beanValue.IsNil() {
+		return false, ErrObjectIsNil
 	}
 
 	if beanValue.Elem().Kind() == reflect.Struct {