I use www in WMT but submitted sitemap without www. Is this detrimental to SEO?

Selected answers from the Dumb SEO Questions Facebook & G+ community.

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  Ranu Jain: Hey Matthew,
  
  Make sure that all the URLs in your sitemap file match the Preferred Domain name. In your case it with www version.
  
  You can replace the submitted sitemap with the new one (with www version).
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  Matthew Stuart: Thank you
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  Tony McCreath: What happens when you visit the non www version? 
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  Luke Ciciliano: I would generate a www version and 301 redirect the old version to it. I would then use Webmaster Tool's "url removal" feature to ask Google to take the old version from the index. Are all your other pages pointing to the www version +Matthew Stuart? ;
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  Matthew Stuart: +Tony McCreath ;I have not set a preference to use either, so it works with or without the www... is that a problem?
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  Tony McCreath: Ideally you want to pick one and always use it consistenty. Having two versions of all your pages can cause things like PageRank and social shares to get split.
  
  To help avoid the other one being used you can set up a site wide 301 redirect. 
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  W.E. Jonk: From the expert panel in this weeks SEO Questions hangout on air on 01:17:25 into the YouTube video: https://dumbseoquestions.com/q/i_use_www_in_wmt_but_submitted_sitemap_without_www_is_this_detrimental_to_seo