title: Enable/Disable button based on input
body: <p>I have an input field for selecting date. I want to apply simple validation that if this field is empty then the submit button should be disabled and enabled when it's filled and it shoud be in sync.</p>
  <p>The date field is having some issue, when I checked through ng-valid it is supposed to give false when nothing is entered into the date field but it's giving true right from the word go.</p>
  <p>I created a simple example using StackBlitz having a single input of date, now I need to disable it when input field is empty and activate it when input is filled.</p>
  <p><a href="https://stackblitz.com/edit/ngx-daterangepicker-material-for-angular8-5ikovy?file=src/app/app.component.html" rel="nofollow noreferrer">https://stackblitz.com/edit/ngx-daterangepicker-material-for-angular8-5ikovy?file=src/app/app.component.html</a></p>