doc: suppress a warning
doc: suppress a warning

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naoa/groonga,redfigure/groonga,cosmo0920/groonga,cosmo0920/groonga,komainu8/groonga,naoa/groonga,kenhys/groonga,groonga/groonga,naoa/groonga,redfigure/groonga,komainu8/groonga,naoa/groonga,kenhys/groonga,hiroyuki-sato/groonga,hiroyuki-sato/groonga,myokoym/groonga,naoa/groonga,groonga/groonga,cosmo0920/groonga,kenhys/groonga,hiroyuki-sato/groonga,groonga/groonga,naoa/groonga,redfigure/groonga,myokoym/groonga,cosmo0920/groonga,komainu8/groonga,kenhys/groonga,cosmo0920/groonga,groonga/groonga,komainu8/groonga,myokoym/groonga,hiroyuki-sato/groonga,groonga/groonga,myokoym/groonga,myokoym/groonga,myokoym/groonga,redfigure/groonga,hiroyuki-sato/groonga,myokoym/groonga,redfigure/groonga,redfigure/groonga,komainu8/groonga,redfigure/groonga,myokoym/groonga,cosmo0920/groonga,kenhys/groonga,groonga/groonga,komainu8/groonga,naoa/groonga,kenhys/groonga,komainu8/groonga,cosmo0920/groonga,kenhys/groonga,cosmo0920/groonga,kenhys/groonga,hiroyuki-sato/groonga,naoa/groonga,groonga/groonga,hiroyuki-sato/groonga,redfigure/groonga,komainu8/groonga,groonga/groonga,hiroyuki-sato/groonga