error Cannot read property 'files' of undefined when upload files

Question

I work on angular 7 project

I face issue when select file then press button upload to get selected file

then it show error Cannot read property 'files' of undefined

as below

DeliverySystemComponent.html:25 ERROR TypeError: Cannot read property 'files' of undefined
    at Object.eval [as handleEvent] (DeliverySystemComponent.html:26)
    at handleEvent (core.js:29239)
    at callWithDebugContext (core.js:30309)
    at Object.debugHandleEvent [as handleEvent] (core.js:30036)
    at dispatchEvent (core.js:19859)
    at core.js:21044
    at SafeSubscriber.schedulerFn [as _next] (core.js:23747)
    at SafeSubscriber.__tryOrUnsub (Subscriber.js:194)
    at SafeSubscriber.next (Subscriber.js:132)
    at Subscriber._next (Subscriber.js:76)
View_DeliverySystemComponent_0 @ DeliverySystemComponent.html:25

and that actually my issue

so How to solve this issue

what I try is

delivery html component

<app-custom-upload #cusUpload nbTooltip="upload excel file" nbTooltipPlacement="bottom"
      nbTooltipStatus="primary" (complete)="handleFileInput($event.target.files)"></app-custom-upload>

<button (click)="uploadFile(files)" class="btn btn-link" style="margin-right: 0px">
          <i nbTooltip="Import Template" nbTooltipPlacement="bottom" nbTooltipStatus="primary">
            <nb-icon icon="cloud-upload-outline"></nb-icon>
          </i>
</button>

delivery component type script

fileToUpload: File = null;
handleFileInput(files: FileList) {
  if (files.length == 0) {
      return;
    }

  this.fileToUpload = files.item(0);

}
public uploadFile = (files) => {

  const formData = new FormData();

  formData.append('file', this.fileToUpload,this.fileToUpload.name);
 }