error MtSQL 1048 can not be null

drop database BaseDatos;
create database if not exists BaseDatos;
use BaseDatos;

create table if not exists genre(
id_genero int not null auto_increment,
nombre_genero varchar (45) not null,
primary key (id_genero))ENGINE=INNODB;

create table if not exists user (
id_usuario int not null auto_increment, 
nombre varchar (45)not null, 
password varchar (45)not null,
primary key (id_usuario))ENGINE=INNODB;
create  table if not exists singer (
id_interprete int not null auto_increment,
nombre_interprete varchar (45)not null,
nacionalidad varchar (45)not null,
primary key (id_interprete))ENGINE=INNODB;
create table if not exists song (
id_cancion int not null auto_increment,
nombre_cancion varchar (45) not null,
id_interprete int not null,
duracion int not null,
tamanio int not null,
id_genero int not null,
primary key (id_cancion),
foreign key (id_interprete)references singer(id_interprete),
foreign key (id_genero)references genre(id_genero) )ENGINE=INNODB;
##########
use BaseDatos;
insert into user(id_usuario,nombre,password) values (NULL,"jor","123");
insert into genre(id_genero,nombre_genero)values (NULL,"");
insert into song(id_cancion,nombre_cancion,duracion,tamanio)values('',"",'','');
insert into singer(id_interprete,nombre_interprete,nacionalidad)values('',"","");

When I execute it, it marks me error 1048