Some whitespace characters bypass zero-length test in query parsers leading to 400 Bad Request

The edismax and some other query parsers treat pure whitespace queries as empty queries, but they use Java's String.trim() method to normalise queries. That method only treats characters 0-32 as whitespace. Other whitespace characters exist - such as U+3000 IDEOGRAPHIC SPACE - which bypass the test and lead to 400 Bad Request responses - see for example /solr/mycollection/select?q=%E3%80%80&defType=edismax vs /solr/mycollection/select?q=%20&defType=edismax. The first fails with the exception:

org.apache.solr.search.SyntaxError: Cannot parse '': Encountered "<EOF>" at line 1, column 0. Was expecting one of: <NOT> ... "+" ... "-" ... <BAREOPER> ... "(" ... "*" ... <QUOTED> ... <TERM> ... <PREFIXTERM> ... <WILDTERM> ... <REGEXPTERM> ... "[" ... "{" ... <LPARAMS> ... "filter(" ... <NUMBER> ... <TERM> ...

PR 1172 updates the dismax, edismax and rerank query parsers to use StringUtils.isWhitespace() which is aware of all whitespace characters.

Prior to the change, rerank behaves differently for U+3000 and U+0020 - with the change, both the below give the "mandatory parameter" message:

q=greetings&rq={!rerank%20reRankQuery=$rqq%20reRankDocs=1000%20reRankWeight=3}&rqq=%E3%80%80 - generic 400 Bad Request

q=greetings&rq={!rerank%20reRankQuery=$rqq%20reRankDocs=1000%20reRankWeight=3}&rqq=%20 - 400 reporting "reRankQuery parameter is mandatory"