Re: Fix duplicate detection for null-treatment window functions

[Tatsuo Ishii]

> V4 looks good to me.

Fix pushed to master and REL_19_STABLE branches.
Thank you!
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Tatsuo Ishii
SRA OSS K.K.
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp