[simplify]

You can use short circuiting instead:

    <div>
      {items.length === 0 &&
        <p>No items.</p>
      }
      {items.length === 1 &&
        <p>Warning: You only have 1 item, at least 2 is required</p>
      }
      {items.map(...)}
    </div>

`false` is not rendered by react, so this code is perfectly fine.