JPA - возникла исключительная ситуация NullPointerException при извлечении значения из переменной экземпляра

Question

Я создаю корпоративное приложение для субъекта, и у меня есть несколько объектов, вставленных в базу данных, все сопоставленные с JPA из следующих классов:

Aula.java, Sessao.java, Instalacao.java

Оба Aula.java и Instalacao.java имеют значение @Entity, а Sessao.java равно @Embeddable, а Instalacao.java.

использует @Embedded. Используемый алгоритм выглядит примерно так:

Я запрашиваю для указания c Aula и внесите в него некоторые изменения. Я запрашиваю спецификацию c Instalacao, создаю новый Sessao с информацией из полученного Aula и добавляю ее в запрашиваемый Instalacao, который имеет список Sessao

Вот некоторые из упомянутых классов:

public void ativarAula(String nome, String instalacao, Calendar inicio, Calendar fim, int maxAlunos)
        throws ApplicationException {

    EntityManager em = emf.createEntityManager();

    AulaCatalog aulaCatalog = new AulaCatalog(em);
    InstalacaoCatalog instalacaoCatalog = new InstalacaoCatalog(em);

    try {
        Instalacao instal = instalacaoCatalog.getInstalacao(instalacao);
        Aula aula = aulaCatalog.getAula(nome);

        em.getTransaction().begin();
        aulaCatalog.activateAula(aula, instal, inicio, fim, maxAlunos);
        em.getTransaction().commit();
    } catch (Exception e) {
        // Exceptions
    } finally {
        em.close();
    }
}

public void activateAula(Aula aula, Instalacao instalacao, Calendar inicio, Calendar fim, int maxAlunos)
        throws ApplicationException {

    // Verifications

    aula.setActivo(true);
    aula.setDataInicio(inicio);
    aula.setDataFim(fim);
    aula.setInstalacao(instalacao);
    aula.setMaxAlunos(maxAlunos);

    createSessoes(aula, instalacao);
}

private void createSessoes(Aula aula, Instalacao instalacao) {

    List<Calendar> datas = aula.getAulaSpecificDates();

    for (Calendar dia : datas) {
        Sessao novaSessao = new Sessao(aula.getNome(), dia, aula.getDuracao(), aula.getMaxAlunos());
        instalacao.setSessao(novaSessao);
    }
}

============ Sessao. java ============

@Embeddable
public class Sessao implements Comparable<Sessao> {

    public static final String DATE = "data";

    public static final String AULA = "nomeAula";

    @Column(nullable = false)
    private String nomeAula;

    @Column(nullable = false)
    @Temporal(TemporalType.TIMESTAMP) private Calendar data;

    @Column(nullable = false)
    private int duracao;

    @Column(nullable = false)
    private int vagas;

    /**
     * Constructor needed by JPA.
     */
    protected Sessao() {
    }

    public Sessao(String nomeAula, Calendar data, int duracao, int vagas) {
        this.nomeAula = nomeAula;
        this.data = data;
        this.duracao = duracao;
        this.vagas = vagas;
    }

//Getters and setters

============ Aula. java =============

@Entity
@NamedQueries({
    @NamedQuery(name=Aula.FIND_BY_NAME,
            query="SELECT a FROM Aula a WHERE a.nomeAula = :" + Aula.NAME),

    @NamedQuery(name=Aula.FIND_BY_MODALIDADE,
                query="SELECT a FROM Aula a WHERE a.modalidade = :" + Aula.MODALITY),

    @NamedQuery(name=Aula.FIND_ATIVAS_BY_MODALIDADE,
                query="SELECT a FROM Aula a WHERE a.modalidade = :" + Aula.MODALITY
                + " AND a.activo = :" + Aula.ACTIVE),
})
public class Aula {

    // Named query name constants
    public static final String FIND_BY_NAME = "Aula.findByName";
    public static final String NAME = "nomeAula";

    public static final String FIND_BY_MODALIDADE = "Aula.findByModalidade";
    public static final String MODALITY = "modalidade";

    public static final String FIND_ATIVAS_BY_MODALIDADE = "Aula.findAtivasByModalidade";
    public static final String ACTIVE = "activo";

    @Id private String nomeAula;

    @ManyToOne @JoinColumn(name = "MODALIDADE", nullable = false)
    private Modalidade modalidade;

    @Column(nullable = false) private LocalTime horaInicio;

    @Column(nullable = false) private int duracao;

    @ElementCollection @CollectionTable(name = "DIAS_SEMANA_AULA")
    private List<DiasSemana> diasSemana;

    private boolean activo;

    private int maxAlunos;

    @Temporal(TemporalType.DATE) private Calendar dataInicio;

    @Temporal(TemporalType.DATE) private Calendar dataFim;

    @ManyToOne @JoinColumn(name = "INSTALACAO")
    private Instalacao instalacao;

    /**
     * Constructor needed by JPA.
     */
    protected Aula() {
    }

    public Aula(String nome, Modalidade modalidade, LocalTime horaInicio, int duracao, List<DiasSemana> diasSemana) {
        this.nomeAula = nome;
        this.modalidade = modalidade;
        this.horaInicio = horaInicio;
        this.duracao = duracao;
        this.diasSemana = diasSemana;
        this.activo = false;
        this.dataInicio = null;
        this.dataFim = null;
        this.instalacao = null;
        this.maxAlunos = 0;
    }
//Getters and setters

===== ======= Instalacao. java =============

@Entity
@NamedQueries({
    @NamedQuery(name=Instalacao.FIND_BY_NAME,
                query="SELECT i FROM Instalacao i WHERE i.nome = :" + Instalacao.NAME),

    @NamedQuery(name=Instalacao.GET_ALL_NAMES,
                query="SELECT i.nome FROM Instalacao i"),

    @NamedQuery(name=Instalacao.FIND_SESSOES_BY_DATE,
                query="SELECT s FROM Instalacao i inner join i.sessoes s"
                + " WHERE i.nome = :" + Instalacao.NAME
                + " AND s.data = :" + Sessao.DATE),

    @NamedQuery(name=Instalacao.FIND_SESSOES_BY_AULA,
                query="SELECT s FROM Instalacao i join i.sessoes s"
                + " WHERE i.nome = :" + Instalacao.NAME)
                + " AND s.nomeAula = :" + Sessao.AULA),

    @NamedQuery(name=Instalacao.FIND_SESSOES_BETWEEN_DATES,
                query="SELECT s FROM Instalacao i join i.sessoes s"
                + " WHERE i.nome = :" + Instalacao.NAME
                + " AND s.data <= :" + Sessao.DATE
                + " AND s.data >= :" + Sessao.DATE),
})
public class Instalacao {

    public static final String FIND_BY_NAME = "Instalacao.findByName";
    public static final String NAME = "nome";

    public static final String GET_ALL_NAMES = "Instalacao.getAllNames";

    public static final String FIND_SESSOES_BY_DATE = "Instalacao.findSessaoByDate";

    public static final String FIND_SESSOES_BY_AULA = "Instalacao.findSessaoByAula";

    public static final String FIND_SESSOES_BETWEEN_DATES = "Instalacao.findSessaoBetweenDates";

    @Id private String nome;

    @Column(nullable = false)
    private int lotacao;

    @Enumerated(EnumType.STRING) @Column(nullable = false)
    private TipoInstalacao tipo;

    @ElementCollection
    @CollectionTable(name = "MODALIDADES_INSTALACAO", joinColumns = @JoinColumn(name = "NOME_INSTALACAO", nullable = false))
    private List<String> modalidades;

    @ElementCollection
    @CollectionTable(name = "SESSOES_INSTALACAO", joinColumns = @JoinColumn(name = "NOME_INSTALACAO", nullable = false))
    private List<Sessao> sessoes;

    protected Instalacao() {
    }

    public Instalacao(String nome, int lotacao, TipoInstalacao tipo, List<String> modalidades) {
        this.nome = nome;
        this.lotacao = lotacao;
        this.tipo = tipo;
        this.modalidades = modalidades;
        this.sessoes = new ArrayList<>();
    }
//Getters and setters

Вот ошибка:

[EL Warning]: 2020-04-21 03:02:48.04--UnitOfWork(1262548561)--Exception [EclipseLink-69] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A NullPointerException was thrown while extracting a value from the instance variable [nomeAula] in the object [business.main.sessao.Sessao].
Internal Exception: java.lang.NullPointerException
Mapping: org.eclipse.persistence.mappings.DirectToFieldMapping[nomeAula-->NOMEAULA]
Descriptor: RelationalDescriptor(business.main.sessao.Sessao --> [])
Erro a ativar aula: Exception [EclipseLink-69] (Eclipse Persistence Services - 2.6.2.v20151217-774c696): org.eclipse.persistence.exceptions.DescriptorException
Exception Description: A NullPointerException was thrown while extracting a value from the instance variable [nomeAula] in the object [business.main.sessao.Sessao].
Internal Exception: java.lang.NullPointerException
Mapping: org.eclipse.persistence.mappings.DirectToFieldMapping[nomeAula-->NOMEAULA]
Descriptor: RelationalDescriptor(business.main.sessao.Sessao --> [])

Если Вам нужна любая информация, просто скажите так!

Спасибо за вашу помощь!