Code viewer doesn't allow to copy blank lines

Reproduction steps:

• Create a page with the following content:

  Line 1
  
  Line 2
  

• Open the page with ?viewer=code
• Copy the content

Expected result:

• The copied content contains the blank line

Obtained result:

• The copied content is the following:

  Line 1
  Line 2
  

This is particularly wrong in XWiki Syntax where blank lines are important.