how to get the value of selectpicker using angle 5?

hello I have a form with fields

<form [formGroup]="addform" (ngSubmit)="RegistrarArticulo()" class="form-horizontal addform">
<div class="form-group">
    <div class="col-sm-7 col-xs-12">
        <label>Marca</label>                                        
        <select formControlName="marca_mobile" name="marca_mobile" (change)="cambiaDatos()" class="selectpicker form-control bs-select-hidden" data-live-search="true" dropdown>
             <option *ngFor="let menu of this._menu.menuesModel" value="1"> {menu.model}}</option>                              
        </select>
    </div>
</div>

<div class="buttons" id="submit">
    <input class="btn btn-primary" value="Submit" type="submit">
</div>
</form>

when I try to see the value of that select it goes empty:

RegistrarArticulo() {
console.log(this.addform);

}

the form model that I have this way:

 this.addform =   new FormGroup({       
    marca_mobile:  new FormControl('')       
  });

and these are the imports that I have:

import { AddListingService } from '../../services/add-listing.service';
import { Component, OnInit } from '@angular/core';
import { FormGroup, FormControl, ReactiveFormsModule } from '@angular/forms';

I CLARIFY THAT IF I REMOVE THE CLASSES THAT THE SELECT HAS IF IT WORKS