case ACTION_TYPE.RATE_BEER:
  const { item, rating } = action.data;
  const beers = state.beers.map((mappedBeer) => {
    if (mappedBeer.id === item.id) {
      return {
        ...mappedBeer,
        rating
      }
    } else {
      return mappedBeer;
    }
  });
  return {
    ...state,
    beers
}

return {
    ...state,
    beers: null
}

const initialState = {
  beers: null
}

const initialState = {
  beers: null
}

case ACTION_TYPE.RATE_BEER:
  const { item, rating } = action.data;
  //add logic here to check if item is not in beers, add it to the state.
  if (!state.beers.some(beer => el.id === item.id))  {
    return {
      ...state,
      beers: state.beers.push({id: item.id, rating})
    }
  }
  //here you're checking to update existing beer rating
  const beers = state.beers.map((mappedBeer) => {
    if (mappedBeer.id === item.id) {
      return {
        mappedBeer.rating = rating ***
      }
    } else {
      return mappedBeer;
    }
  });

  return {
    ...state,
    beers
}