Attempt to invoke virtual method 'void

Good night, I can not solve the problem, it says that it has an object not referenced (null object reference), but it does not have to initialize the following code:

public void deletar(int id)
    {
        conn.delete("RESULTADO", "_id = ?", new String[] { String.valueOf(id)});
    }

He says it's here! The error: Attempt to invoke virtual method 'void project.henry.count.domain.repoResult.deletar (int)' on a null object reference .

The code that uses this method:

Button btnApagar;
...
    btnApagar = (Button) findViewById(R.id.btnApagar);
    btnApagar.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            try{
                repoResultado.deletar(dados.getId());
            } catch (Exception ex){
                mensagem("ERRO: " + ex.getMessage());
            }
        }
    });