Make sure to add such a change field with an empty string value to the
UpdateRequest (towards the Elasticsearch index) in the first place.
Elasticsearch does support fields with empty string values. The below
Issue was considering the opposite as a possibility. There is therefore
no need anymore to consider using a sentinel value as proposed in the
original Issue (below). This change aims at permanently solving that.
Remove the no longer needed FileWithNoExtensionInElasticPredicate class.
The latter, as well as the removed AbstractQueryChangesTest::byDirectory
test method implementation parts, lead to reverting to the previous
implementation for these tests. -Issue has the references and context.
Bug: Issue 10889
Change-Id: Iec126e4c2456e68d141eb0b8b55f03ede01dcb95
b54caf7da5