Empty result set throws nullpointer for querySingle

[bhowell2]

Version

3.5.0

Context

A query that returns an empty resultset (with querySingle and querySingleWithParams) will cause a NullPointerException.

Here's the code in SQLOperations.java:

  default SQLOperations querySingle(String sql, Handler<AsyncResult<JsonArray>> handler) {
    return query(sql, execute -> {
      if (execute.failed()) {
        handler.handle(Future.failedFuture(execute.cause()));
      } else {
        final ResultSet rs = execute.result();
        if (rs == null) {
          handler.handle(Future.succeededFuture());
        } else {

// NOTE HERE: 
// The result set may not be null, but may be empty. The call to results.get(0) will cause an NPE.
          List<JsonArray> results = rs.getResults();
          if (results == null) {
            handler.handle(Future.succeededFuture());
          } else {
            handler.handle(Future.succeededFuture(results.get(0)));
          }
        }
      }
    });
  }

This fix may be simple in that all that needs to be checked is adding:
if (results == null || results.size() == 0) (and then return Future.succeededFuture()), or this may be a bit deeper of an issue in that ResultSet is not expected to return an empty list if there were no results in the database for the query? (I'd imagine this is okay, but checking here to make sure because of the way this was written.) Future.succeededFuture() is going to return a null result, is this desirable?

[leokongwq]

Why the bug has not been fixed？

[bhowell2]

Probably because I didn't post it to vertx-dev google groups. Posted it there now. The fix is pretty easy, but I wasn't sure which way they wanted to take it.

[pmlopes]

Fixed by aa72de8