Empty elements

I've got a document that looks similar to below:

<message_wrapper>
  <msg_header>
    <token>a token</token>
    <language>a language</language>
  </msg_header
  <msg_body>
    <group>
      <element1>value 1</element1>
      <element2>value 2</element2>
    </group>
     <group>
      <element1>value 3</element1>
      <element2>value 4</element2>
    </group>
    <group>
      <element1></element1>
      <element2></element2>
    </group>
    <group>
      <element1></element1>
      <element2></element2>
    </group>
  </msg_body>
</message_wrapper>

How can I remove the empty groups ?
message_wrapper & msg_body will always have the same names, but the names of
the group & element* elements will not always be the same.

TIA


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