title: Type error when saving FormData when using Redux toolkit
body: <p>I've tried to save FormData(Javascript's standard API) using redux toolkit.</p>
  <pre><code>const initialState{
   myFile: FormData | null
  }
  
  
  const controllerSlice = createSlice({
    name: 'controller',
    initialState,
    reducers: {
      test: (state, action) =&gt; ({
        ...state,
      }),
  //...
  </code></pre>
  <p>It complains</p>
  <p><code>Types of property 'myFile' are incompatible. Type 'WritableDraft&lt;FormData&gt; | null' is not assignable to type 'FormData | null'</code></p>
  <p>I don't know why it complains exactly, but redux toolkit uses immerjs inside of it so seems it wraps FormData with WritableDraft.</p>
  <p>The only solution what I've found is changing <code>FormData | null</code> to <code>any</code></p>
  <pre><code>const initialState{
   myFile: any
  }
  </code></pre>
  <p>But I want to use <code>FormData | null</code> as a type of myFile. Any ideas?</p>