I am getting the following error in Angular 4 :

> 
> ERROR TypeError: Cannot read property 'invalid' of undefined
> 
> 
> 

Here's the code :

```
<form name="form"  #f="ngForm" novalidate>

  <tr>
     <td width="10%" class="text-blue"></td> 
     <td><input type="text"  name="bankname" maxlength="25" appRestrictinput ="words" [(ngModel)]="model.bk_name" #bk_name="ngModel"  class="form-control" autofocus  /> </td>
  </tr>
  <div *ngIf="bankname.invalid && (bankname.dirty || bankname.touched)" class="alert alert-danger">
     <div *ngIf="bankname.errors.required">Name is required</div>
  </div>

</form>

```

Please let me know where I'm going wrong. Thanks in advance.