code: func GetExtensionManager(c *vim25.Client) (*ExtensionManager, error) {
  	if c.ServiceContent.ExtensionManager == nil {
  		return nil, ErrNotSupported
  	}
  	return NewExtensionManager(c), nil
  }
docs: // GetExtensionManager wraps NewExtensionManager, returning ErrNotSupported
  // when the client is not connected to a vCenter instance.