XML error when using `literalAsciiDoc`

The following defaultText produces an XML error:

defaultText = nvim.nmd.literalAsciiDoc ''
  testing
'';

But not:

defaultText = nvim.nmd.literalAsciiDoc ''
  testing'';

Putting the '' on a new line seems to be producing a simpara tag rather than a para.

<para><emphasis>Default:</emphasis> testing</simpara>

and the error:

/nix/store/4q49zgv4217b51lps4qx378q6hrwvzbl-nmd-documents/nmd-result/neovim-flake-options.xml:430: parser error : Opening and ending tag mismatch: para line 430 and simpara
pe:</emphasis> string</para><para><emphasis>Default:</emphasis> testing</simpara