Reset or Clean button for ion-select and ion-option

Basically, how can i clean a ionic select with a button? I’ve try doing this.escolhido = null but get me this error:

“ERROR Error: Query: First argument passed to startAt(), endAt(), or equalTo() cannot be an object.”

I understand the error and why its happening but how can i fix it? Here is my codes:


  <ion-navbar color="amarelo">
    <ion-buttons left>
      <button ion-button icon-only menuToggle>
        <ion-icon name="menu"></ion-icon>

    <ion-title >


<ion-content padding>
          <ion-select (ionChange)="onContextChange($event)" [(ngModel)]="escolhido"
          cancelText="Cancelar" okText="Ok">
          <ion-option *ngFor="let gene of genesList$ | async"
        <button ion-button (click)="limpaFiltro()" color="amarelo">
            <ion-list-header class="estilo">
            <ng-container *ngFor="let prod of prodsList$ | async | slice:0:show; let i=index">
                detail-push navPush="ViewProdPage"[navParams]="{prod:prod}">
      <button full ion-button (click)="loadMore()" color="amarelo">
        Carregar mais

    <ion-fab bottom right>
        <button color="amarelo" ion-fab navPush="AddProdPage"><ion-icon name="add"></ion-icon></button>


import { Component } from '@angular/core';
import { IonicPage, NavController, NavParams } from 'ionic-angular';
import { Producao } from '../../models/producao';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';
import { ProducoesProvider } from '../../providers/producoes/producoes'
import { Genero } from '../../models/genero';

 * Generated class for the AdminPage page.
 * See for more info on
 * Ionic pages and navigation.

  selector: 'page-admin',
  templateUrl: 'admin.html',
export class AdminPage {

  public show: number;
  escolhido: Object;
  prodsList$: Observable<Producao[]>;
  genesList$: Observable<Genero[]>;

  constructor(public navCtrl: NavController, public navParams: NavParams, 
    private producoesProvider: ProducoesProvider) { = 5;

      this.prodsList$ = this.producoesProvider.getProdsList().valueChanges();

    this.genesList$ = this.producoesProvider.getGenesList().valueChanges();

    this.escolhido = null;

  loadMore() { += 5;

  onContextChange(ctxt: string): void {
    this.prodsList$ = this.producoesProvider.assembleGeneroFilteredList(ctxt).valueChanges();