code: private function getConfigValue($config, $language, $key)
      {
          if (!isset($config[$key]) || empty($config[$key])) {
              if (isset($this->defaults[$language][$key])) {
                  return $this->defaults[$language][$key];
              }
  
              return array();
          }
  
          if (!is_array($config[$key])) {
              return array($config[$key]);
          }
  
          return $config[$key];
      }
docs: Get command lines to add for a configuration value in .travis.yml file
  
  @param array  $config   Configuration of travis ci parsed
  @param string $language Language for getting the default value if no value is set
  @param string $key      Configuration key
  
  @return array A list of command to add to Dockerfile