TypeError: Cannot read property 'username' of undefined in [register.username in RegisterPage@15:19]

<ion-navbar *navbar>
  <ion-title>Register</ion-title>
</ion-navbar>

<ion-content class="login-page">

  <ion-list>
    <div class="logo">
      <img src="img/appicon.svg">
    </div>

    <form #signupForm="ngForm" novalidate>
      <ion-item>
        <ion-label floating primary>Username</ion-label>
        <ion-input [(ngModel)]="register.username" ngControl="username" type="text" #username="ngForm" required>
        </ion-input>
      </ion-item>
      <p [hidden]="username.valid || submitted == false" danger padding-left>
        Username is required
      </p>

      <ion-item>
        <ion-label floating primary>Password</ion-label>
        <ion-input [(ngModel)]="register.password" ngControl="password" type="password" #password="ngForm" required>
        </ion-input>
      </ion-item>
      <p [hidden]="password.valid || submitted == false" danger padding-left>
        Password is required
      </p>

      <div padding>
        <button (click)="onSignup(signupForm)" type="submit" primary block>Create</button>
      </div>
    </form>
  </ion-list>

</ion-content>