How can get default return values for a SPARQL query when counting

Question

I have a query where I count with a grouping on years. For some of the years there is no items to count and thus no result. I would like to have SPARQL return a count of zero for such years.

I am using the Wikidata Query Service, https://query.wikidata.org, and my present solution is to make a series of values and a union with the actual query. It looks a bit clumsy to me. Is there a better way?

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select ?year ?number_of_pages ?work_label where {
  {
    select ?year (sample(?pages) as ?number_of_pages) ?work_label       
    where {
      {
        select * where {
          values (?year ?pages ?work_label) {
            ("2000" "0"^^xsd:integer "_") 
            ("2001" "0"^^xsd:integer "_") 
            ("2002" "0"^^xsd:integer "_") 
            ("2003" "0"^^xsd:integer "_") 
            ("2004" "0"^^xsd:integer "_") 
            ("2005" "0"^^xsd:integer "_") 
            ("2006" "0"^^xsd:integer "_") 
            ("2007" "0"^^xsd:integer "_") 
            ("2008" "0"^^xsd:integer "_") 
            ("2009" "0"^^xsd:integer "_") 
            ("2010" "0"^^xsd:integer "_") 
            ("2011" "0"^^xsd:integer "_")
            ("2012" "0"^^xsd:integer "_")
            ("2013" "0"^^xsd:integer "_")
            ("2014" "0"^^xsd:integer "_")
            ("2015" "0"^^xsd:integer "_")
            ("2016" "0"^^xsd:integer "_")
          }
        }
      }
      union {
        ?work wdt:P50 wd:Q18921408 .
        ?work wdt:P1104 ?pages .
        ?work wdt:P577 ?date . 
        ?work rdfs:label ?long_work_label . filter(lang(?long_work_label) = 'en')
        bind(substr(?long_work_label, 1, 20) as ?work_label)
        bind(str(year(?date)) as ?year) 
      }
    } 
    group by ?year ?work ?work_label
    order by ?year 
  }
}