Attempt to invoke virtual method on a null object reference [closed]

Error:

09-12 17:13:09.088
26022-26022/costamilam.guilherme.contatosempresariais
E/AndroidRuntime: FATAL EXCEPTION: main
   Process: costamilam.guilherme.contatosempresariais, PID: 26022
   java.lang.NullPointerException: Attempt to invoke virtual method 'int
android.database.sqlite.SQLiteDatabase.update(java.lang.String,
android.content.ContentValues, java.lang.String, java.lang.String[])'
on a null object reference
       at costamilam.guilherme.contatosempresariais.ContatoDAO.alterar(ContatoDAO.java:83)
       at costamilam.guilherme.contatosempresariais.TelaDetalhe$1.onClick(TelaDetalhe.java:153)
       at android.view.View.performClick(View.java:5076)
       at android.view.View$PerformClick.run(View.java:20279)
       at android.os.Handler.handleCallback(Handler.java:739)
       at android.os.Handler.dispatchMessage(Handler.java:95)
       at android.os.Looper.loop(Looper.java:135)
       at android.app.ActivityThread.main(ActivityThread.java:5910)
       at java.lang.reflect.Method.invoke(Native Method)
       at java.lang.reflect.Method.invoke(Method.java:372)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)

09-12 17:26:05.946
26198-26198/costamilam.guilherme.contatosempresariais
E/AndroidRuntime: FATAL EXCEPTION: main
   Process: costamilam.guilherme.contatosempresariais, PID: 26198
   java.lang.NullPointerException: Attempt to invoke virtual method 'int
android.database.sqlite.SQLiteDatabase.delete(java.lang.String,
java.lang.String, java.lang.String[])' on a null object reference
       at costamilam.guilherme.contatosempresariais.ContatoDAO.deletar(ContatoDAO.java:90)
       at costamilam.guilherme.contatosempresariais.TelaDetalhe$2.onClick(TelaDetalhe.java:172)
       at android.view.View.performClick(View.java:5076)
       at android.view.View$PerformClick.run(View.java:20279)
       at android.os.Handler.handleCallback(Handler.java:739)
       at android.os.Handler.dispatchMessage(Handler.java:95)
       at android.os.Looper.loop(Looper.java:135)
       at android.app.ActivityThread.main(ActivityThread.java:5910)
       at java.lang.reflect.Method.invoke(Native Method)
       at java.lang.reflect.Method.invoke(Method.java:372)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1405)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)

Screen:

public class TelaDetalhe extends AppCompatActivity {

private ContatoDAO cDAO; //Instancia da classe DAO

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_tela_detalhe);

    final Contato c = (Contato) getIntent().getSerializableExtra("contato");

    btnAtualizar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            long contatoId = c.getId();

            c.setId(contatoId);
            c.setNome(etNome.getText().toString());
            c.setTelefone(etTelefone.getText().toString());
            c.setEmpresa(etEmpresa.getText().toString());
            c.setBrunko(cbBrunko.isChecked());
            c.setCarter(cbCarter.isChecked());
            c.setFortmetal(cbFortmetal.isChecked());
            c.setMerco(cbMerco.isChecked());
            c.setMetan(cbMetan.isChecked());
            c.setNdflex(cbNdflex.isChecked());
            c.setNotus(cbNotus.isChecked());
            c.setRiosulense(cbRiosulense.isChecked());
            c.setYming(cbYiming.isChecked());
            c.setMesContato(spMesContato.getSelectedItemPosition());
            c.setAnoContato(spAnoContato.getSelectedItem().toString());

            cDAO = new ContatoDAO(TelaDetalhe.this);
            cDAO.alterar(c);

            Toast.makeText(getBaseContext(), "Contato alterado com sucesso!", Toast.LENGTH_LONG).show();
        }
    });

    btnDeletar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            //Removendo do Banco
            cDAO = new ContatoDAO(TelaDetalhe.this);
            cDAO.deletar(c.getId());

            Toast.makeText(getBaseContext(), "Contato excluído com sucesso!", Toast.LENGTH_LONG).show();
        }
    });

}
}

DAO:

public class ContatoDAO {

private SQLiteDatabase database;
private BaseDAO dbHelper;

public ContatoDAO(Context contexto){
    dbHelper = new BaseDAO(contexto);
}

public void abrirBanco() {
    database = dbHelper.getWritableDatabase();
}

public void fecharBanco() {
    dbHelper.close();
}

//Alterar
public long alterar(Contato c) {
    long id = c.getId();

    ContentValues cv = new ContentValues();

    cv.put(BaseDAO.CONTATO_NOME, c.getNome());
    cv.put(BaseDAO.CONTATO_TELEFONE, c.getTelefone());
    cv.put(BaseDAO.CONTATO_EMPRESA, c.getEmpresa());
    cv.put(BaseDAO.CONTATO_BRUNKO, c.isBrunko());
    cv.put(BaseDAO.CONTATO_CARTER, c.isCarter());
    cv.put(BaseDAO.CONTATO_FORTMETAL, c.isFortmetal());
    cv.put(BaseDAO.CONTATO_MERCO, c.isMerco());
    cv.put(BaseDAO.CONTATO_METAN, c.isMetan());
    cv.put(BaseDAO.CONTATO_NDFLEX, c.isNdflex());
    cv.put(BaseDAO.CONTATO_NOTUS, c.isNotus());
    cv.put(BaseDAO.CONTATO_RIOSULENSE, c.isRiosulense());
    cv.put(BaseDAO.CONTATO_YIMING, c.isYming());
    cv.put(BaseDAO.CONTATO_MES_CONTATO, c.getMesContato());
    cv.put(BaseDAO.CONTATO_ANO_CONTATO, c.getAnoContato());

    return database.update(BaseDAO.TABELA_AGENDA, cv, BaseDAO.CONTATO_ID + "=?", new String[]{String.valueOf(id)});
}

//Deletar
public long deletar(long id) {
    long identificador = id;

    return database.delete(BaseDAO.TABELA_AGENDA, BaseDAO.CONTATO_ID + "=?", new String[]{String.valueOf(identificador)});
}
}