Fixes querying with inline map when a value is nil

This changes the inline map query build condition to use `IS NULL` 
instead of the equality operator when the provided value is `nil`.

query_test.go

@@ -207,10 +207,12 @@ func TestSearchWithStruct(t *testing.T) {
 }
 
 func TestSearchWithMap(t *testing.T) {
+	productID := 1
 	user1 := User{Name: "MapSearchUser1", Age: 1, Birthday: now.MustParse("2000-1-1")}
 	user2 := User{Name: "MapSearchUser2", Age: 10, Birthday: now.MustParse("2010-1-1")}
 	user3 := User{Name: "MapSearchUser3", Age: 20, Birthday: now.MustParse("2020-1-1")}
-	DB.Save(&user1).Save(&user2).Save(&user3)
+	user4 := User{Name: "MapSearchUser4", Age: 30, Birthday: now.MustParse("2020-1-1"), ProductID: &productID}
+	DB.Save(&user1).Save(&user2).Save(&user3).Save(&user4)
 
 	var user User
 	DB.First(&user, map[string]interface{}{"name": user1.Name})
@@ -234,6 +236,21 @@ func TestSearchWithMap(t *testing.T) {
 	if len(users) != 1 {
 		t.Errorf("Search all records with inline map")
 	}
+
+	DB.Find(&users, map[string]interface{}{"name": user4.Name, "product_id": nil})
+	if len(users) != 0 {
+		t.Errorf("Search all records with inline map containing null value finding 0 records")
+	}
+
+	DB.Find(&users, map[string]interface{}{"name": user1.Name, "product_id": nil})
+	if len(users) != 1 {
+		t.Errorf("Search all records with inline map containing null value finding 1 record")
+	}
+
+	DB.Find(&users, map[string]interface{}{"name": user4.Name, "product_id": productID})
+	if len(users) != 1 {
+		t.Errorf("Search all records with inline multiple value map")
+	}
 }
 
 func TestSearchWithEmptyChain(t *testing.T) {
@@ -377,10 +394,15 @@ func TestNot(t *testing.T) {
 	DB.Create(getPreparedUser("user1", "not"))
 	DB.Create(getPreparedUser("user2", "not"))
 	DB.Create(getPreparedUser("user3", "not"))
-	DB.Create(getPreparedUser("user4", "not"))
+
+	user4 := getPreparedUser("user4", "not")
+	productID := 1
+	user4.ProductID = &productID
+	DB.Create(user4)
+
 	DB := DB.Where("role = ?", "not")
 
-	var users1, users2, users3, users4, users5, users6, users7, users8 []User
+	var users1, users2, users3, users4, users5, users6, users7, users8, users9 []User
 	if DB.Find(&users1).RowsAffected != 4 {
 		t.Errorf("should find 4 not users")
 	}
@@ -423,15 +445,20 @@ func TestNot(t *testing.T) {
 		t.Errorf("Should find all users's name not equal 3")
 	}
 
-	DB.Not("name", []string{"user3"}).Find(&users7)
+	DB.Not(map[string]interface{}{"name": "user3", "product_id": nil}).Find(&users7)
-	if len(users1)-len(users7) != int(name3Count) {
+	if len(users7) != 1 {
+		t.Errorf("Should find all user's name not equal to 3 who do not have product ids")
+	}
+
+	DB.Not("name", []string{"user3"}).Find(&users8)
+	if len(users1)-len(users8) != int(name3Count) {
 		t.Errorf("Should find all users's name not equal 3")
 	}
 
 	var name2Count int64
 	DB.Table("users").Where("name = ?", "user2").Count(&name2Count)
-	DB.Not("name", []string{"user3", "user2"}).Find(&users8)
+	DB.Not("name", []string{"user3", "user2"}).Find(&users9)
-	if len(users1)-len(users8) != (int(name3Count) + int(name2Count)) {
+	if len(users1)-len(users9) != (int(name3Count) + int(name2Count)) {
 		t.Errorf("Should find all users's name not equal 3")
 	}
 }

scope_private.go

@@ -31,7 +31,11 @@ func (scope *Scope) buildWhereCondition(clause map[string]interface{}) (str stri
 	case map[string]interface{}:
 		var sqls []string
 		for key, value := range value {
+			if value != nil {
 				sqls = append(sqls, fmt.Sprintf("(%v = %v)", scope.Quote(key), scope.AddToVars(value)))
+			} else {
+				sqls = append(sqls, fmt.Sprintf("(%v IS NULL)", scope.Quote(key)))
+			}
 		}
 		return strings.Join(sqls, " AND ")
 	case interface{}:
@@ -97,7 +101,11 @@ func (scope *Scope) buildNotCondition(clause map[string]interface{}) (str string
 	case map[string]interface{}:
 		var sqls []string
 		for key, value := range value {
+			if value != nil {
 				sqls = append(sqls, fmt.Sprintf("(%v <> %v)", scope.Quote(key), scope.AddToVars(value)))
+			} else {
+				sqls = append(sqls, fmt.Sprintf("(%v IS NOT NULL)", scope.Quote(key)))
+			}
 		}
 		return strings.Join(sqls, " AND ")
 	case interface{}: