title: how to create empty koalas df
body: <p>I am trying to create empty Koalas DataFrame using the following command</p>
  <pre><code>df = ks.from_pandas(pd.DataFrame(columns=['A', 'B', 'C']))
  </code></pre>
  <p>But I am getting the following error</p>
  <p><code>ValueError: can not infer schema from empty or null dataset</code></p>
  <p>I tried following command too, but found the similar error</p>
  <pre><code>df = ks.DataFrame(columns=['col1', 'col2'])
  </code></pre>
  <p>I would really appreciate if someone can help me with this.</p>