fix(lesson): fixed merge errors

model/web/error_code.go

@@ -12,6 +12,8 @@ const (
 	FacultyNotExist    string = "FACULTY_NOT_EXIST"
 	MajorNotExist      string = "MAJOR_NOT_EXIST"
 	CourseNotExist     string = "COURSE_NOT_EXIST"
+	LessonNotExist     string = "LESSON_NOT_EXIST"
+	LessonMaterialNotExist string = "LESSON_MATERIAL_NOT_EXIST"
 	IDExists           string = "ID_ALREADY_EXISTS"
 	NotExist           string = "NOT_EXIST"