code: func (c *ConfigFile) MustInt64(section, key string, defaultVal ...int64) int64 {
  	value, err := c.Int64(section, key)
  	if len(defaultVal) > 0 && err != nil {
  		return defaultVal[0]
  	}
  	return value
  }
docs: // MustInt64 always returns value without error,
  // it returns 0 if error occurs.