What version of SonarQube are you using now ?
The error happens because NewRule.setDebtSubCharacteristic has been removed a few months ago from Sonar products. This method was deprecated since SonarQube 5.5 (early 2016)!
It appears that one plugin installed on your server still uses this old API. A similar error was recently reported in this thread.
I would recommend the same solution, contact the maintainers to update the plugin or remove it if you don’t really use it.
Thanks for reporting!