title: JSZip 3.7.1 parameter issue
body: <p>I started getting this bellow error after I updated JSZip version from <code>3.1.5</code> to <code>3.7.1</code>. Below is the the piece of code and the error I'm getting.</p>
  <pre><code>images.forEach((image, i) =&gt; {
      img.file(`${this.props.currentRule.DashboardName[i]}.png`, image, {
        base64: true,
      });
    });
  </code></pre>
  <blockquote>
  <p>ERROR in [at-loader]
  ./src/client/components/modals/exportModal/ExportModal.tsx:84:68
  TS2769: No overload matches this call.   Overload 1 of 4, '(path: string, data: string | Blob | number[] | Uint8Array | ArrayBuffer |
  ReadableStream | Promise&lt;string | Blob | number[] | Uint8Array |
  ArrayBuffer | ReadableStream&gt;, options?: JSZipFileOptions): JSZip',
  gave the following error.
  Argument of type 'unknown' is not assignable to parameter of type 'string | Blob | number[] | Uint8Array | ArrayBuffer | ReadableStream
  | Promise&lt;string | Blob | number[] | Uint8Array | ArrayBuffer  |
  ReadableStream&gt;'.
  Type '{}' is missing the following properties from type 'Promise&lt;string | Blob | number[] | Uint8Array | ArrayBuffer |
  ReadableStream&gt;': then, catch, [Symbol.toStringTag], finally<br />
  Overload 2 of 4, '(path: string, data: null, options?:
  JSZipFileOptions &amp; { dir: true; }): JSZip', gave the following error.
  Argument of type 'unknown' is not assignable to parameter of type 'null'. SZipFileOptions): JSZip', gave the following error.
  Argument of type 'unknown' is not assignable to parameter of type 'string | Blob | number[] | Uint8Array | ArrayBuffer | ReadableStream
  | Promise&lt;string | Blob | number[] | Uint8Array | ArrayBuffer  |
  ReadableStream&gt;'.
  Type '{}' is missing the following properties from type 'Promise&lt;string | Blob | number[] | Uint8Array | ArrayBuffer |
  ReadableStream&gt;': then, catch, [Symbol.toStringTag], finally<br />
  Overload 2 of 4, '(path: string, data: null, options?:
  JSZipFileOptions &amp; { dir: true; }): JSZip', gave the following error.
  Argument of type 'unknown' is not assignable to parameter of type 'null'.</p>
  </blockquote>
  <p>Can someone please help me with this?</p>