[Checkins] [zopefoundation/Products.ZCatalog] a47ebc: Fix EmptyValue support

[Andreas Gabriel]

  Branch: refs/heads/notindexed_value_support
  Home:   https://github.com/zopefoundation/Products.ZCatalog
  Commit: a47ebc7d664f6922d7ad96000974e38d019a63f6
      https://github.com/zopefoundation/Products.ZCatalog/commit/a47ebc7d664f6922d7ad96000974e38d019a63f6
  Author: Andreas Gabriel <gabriel at hrz.uni-marburg.de>
  Date:   2019-05-07 (Tue, 07 May 2019)

  Changed paths:
    M src/Products/PluginIndexes/KeywordIndex/KeywordIndex.py
    M src/Products/PluginIndexes/unindex.py

  Log Message:
  -----------
  Fix EmptyValue support