Remove unwanted empty by using XSLT

I want to remove unwanted empty tags from HTML file by using XSLT.

<p>
    <span> </span>
  </p>
  <p>
    <span> </span>
  </p>
  <p>
    <span>Evaluation Warning : The document was created with Spire.Doc for .NET.</span>
  </p>

I need output like this

 <p>
    <span>Evaluation Warning : The document was created with Spire.Doc for .NET.</span>
  </p>

Thanks In Advance.