Report error if schema null. (vesoft-inc#1700) (vesoft-inc#1711)

Co-authored-by: dutor <440396+dutor@users.noreply.github.com>
(cherry picked from commit 8a9daec)
(cherry picked from commit 65364c2)

Co-authored-by: CPWstatic <13495049+CPWstatic@users.noreply.github.com>

Add StatsManager in graphd (vesoft-inc#1301)

Issue vesoft-inc#1203 fixed the possible crash. (vesoft-inc#1204)

The crash is caused by the use of two meaningless DCHECK in debug mode.

Fixed ConfigTest occasional failure (vesoft-inc#770)

readme delete email (vesoft-inc#374)