code: protected function checkAndGetBusters()
      {
          // if no bustersJson, exception
          if ($this->fileSystem->fileExists($this->config['bustersJsonPath']) === false) {
              throw new LengthException('busters json not found.');
          }
  
          // get busters json and decode it
          $bustersJson = $this->fileSystem->getFile($this->config['bustersJsonPath']);
          if ($bustersJson == '') {
              throw new UnderflowException('busters json is empty.');
          }
          $busters = json_decode($bustersJson);
  
          // is it valid json?
          if (json_last_error() !== JSON_ERROR_NONE) {
              throw new UnexpectedValueException('bustersJson is invalid JSON.');
          }
  
          return $busters;
      }
docs: Check for errors in busters.json
  
  @throws LengthException          if the busters.json file is not found
  @throws UnderflowException       if the busters.json file contents are empty
  @throws UnexpectedValueException if the busters.json has text but is not
  @return array                    the parsed json in busters.json