Major Description
When an empty RegexCompletionQuery is provided to ContextQuery, the following assertion failure occurs:
java.lang.AssertionError: input should not end with the context separator at org.apache.lucene.search.suggest.document.ContextQuery$ContextCompletionWeight.setInnerWeight(ContextQuery.java:296) at org.apache.lucene.search.suggest.document.ContextQuery$ContextCompletionWeight.setNextMatch(ContextQuery.java:275) at org.apache.lucene.search.suggest.document.NRTSuggester.lookup(NRTSuggester.java:221) at org.apache.lucene.search.suggest.document.CompletionScorer.score(CompletionScorer.java:70) at org.apache.lucene.search.BulkScorer.score(BulkScorer.java:39) at org.apache.lucene.search.suggest.document.SuggestIndexSearcher.suggest(SuggestIndexSearcher.java:78) at org.apache.lucene.search.suggest.document.SuggestIndexSearcher.suggest(SuggestIndexSearcher.java:58) at org.apache.lucene.search.suggest.document.TestContextQuery.testEmptyRegexQuery(TestContextQuery.java:193)
This is a bit of an edge case, but may be concerning since without assertions enabled, you can go on to access IntsRef indices that are out of bounds.
The attached patch provides a reproduction of the issue, as the test case TestContextQuery#testEmptyRegexQuery. Note that to reproduce, Java assertions must be enabled (as in the default configuration for tests).
The patch also provides a test case for the normal behavior of an empty RegexCompletionQuery, when it is not wrapped in ContextQuery (TestRegexCompletionQuery#testEmptyRegexQuery). In this case, there is no error, and all suggestions are returned.
