Troubleshoot problems scanned by SpotBugs

[marsishandsome]

[zz-jason]

could you post the original soptbugs reports in the issue description to help us get a deeper understanding of the issues? BTW, it would be better if you can put the instructions about how to generate the report in the issue description.

[iosmanthus]

There is a report generated by spotbugs' maven-plugin: https://gist.github.com/iosmanthus/55f861b45f952c4b1393f4dcfba13f77