GenerationType.IDENTITY Null값 허용 안 되는 에러

안녕하세요. 기본 키 맵핑에서 GenerationType.IDENTITY 관련 부분 질문드립니다.

GenerationType.IDENTITY는 PK를 입력하지 않아도 auto increment라고 해서 저절로 생성되는 거 아닌가요?

그런데 이런 에러가 떴습니다.
ERROR: NULL not allowed for column "ID"; SQL statement:

답변 부탁드리겠습니다. 감사합니다!

package hellojpa;

import javax.persistence.*;


@Entity
public class Member {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;
    @Column(name = "name")
    private String username;


    public Member() { // 기본 생성자가 하나 있어야 함
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

package hellojpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;
import javax.transaction.Transaction;

public class JpaMain {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
        // EntityManagerFactory는 application 로딩 시점에 딱 하나만 만들어놔야 한다.
        // Transaction 단위로 EntityManager를 만든다.
        EntityManager em = emf.createEntityManager(); // 쉽게 생각하면 데이터베이스 connection을 하나 받았다고 생각할 수 있음.

        EntityTransaction tx = em.getTransaction();
        tx.begin();

        try{
            Member member = new Member();
            member.setUsername("Opeahchsdf");

            em.persist(member);

            tx.commit();
        } catch (Exception e) {
            tx.rollback();
        } finally {
            em.close(); // 끝나면 반드시 닫아줘야 함
        }

        emf.close();
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.2"
             xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_2.xsd">
    <persistence-unit name="hello">
        <properties>
            <!-- 필수 속성 -->
            <property name="javax.persistence.jdbc.driver" value="org.h2.Driver"/>
            <property name="javax.persistence.jdbc.user" value="sa"/>
            <property name="javax.persistence.jdbc.password" value=""/>
            <property name="javax.persistence.jdbc.url" value="jdbc:h2:tcp://localhost/~/test"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
            <!-- 옵션 -->
            <property name="hibernate.show_sql" value="true"/>
            <property name="hibernate.format_sql" value="true"/>
            <property name="hibernate.use_sql_comments" value="true"/>
            <property name="hibernate.hbm2ddl.auto" value="create" />
        </properties>
    </persistence-unit>
</persistence>