Error "Tag XML needed in sitemap" if the site does not have pages with sitemap active

• Type: Bug
• Status: Closed
• Resolution: Fixed
• Affects Version/s: 6.2.X EE, 7.0.X, Master
• Fix Version/s: 7.0.0 DXP FP52, 7.0.0 DXP SP9, 7.0.X, 7.1.10 DXP FP1, 7.1.X, Master
• Component/s: SEO Tools > OpenGraph tags
• Labels:
  • ee-ts
  • liferay-dxp-70-sp9
  • liferay-fixpack-de-52-7010
  • liferay-fixpack-dxp-1-7110
• Branch Version/s:
  7.0.x
• Backported to Branch:
  Committed
• Story Points: 5
• Fix Priority: 2
• Git Pull Request: https://github.com/brianchandotcom/liferay-portal/pull/60480

When sitemap has only a empty urlset it gives validation errors.
https://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd

Steps to reproduce:

1. Create a site;
2. Create 2 pages;
3. Disable sitemap on each page;
4. look for the sitemap preview;

Expected Results:
No XML should be generareted.

Actual Results:
The portal generate a XML as follow:

<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml"/>

Reproduced on 6.2.x:
Commit da7ba9014fa6ba030ede86f2cd944ad00fd83df5 - Thu Jun 7 13:36:10 2018 +0200
Reproduced on 7.0.x: (must test the individual page sitemap.xml)
Commit: 0b500a9d3b0f3f401d0c40edb6fa372f0e8dfcb2
Base Branch Commit: 7014765d298eebacb143b2ddf15237b964591639
Updated on: Thu Jun 7 22:01:25 2018 -0700*
Reproduced on Master: (must test the individual page sitemap.xml)
Commit: 56fa1da59ae4e78db17dbe0749a5ccb02826928f
Updated on: Fri Jun 8 13:55:48 2018 -0700