The voluntary vendor of the goodwill of a business will not be allowed to solicit the customers of such business and will be restrained from doing any acts which will enable him or her to do so. But he or she cannot, in the absence of express agreement, be restrained from carrying on a similar business on his or her own account; and a bankrupt, the goodwill of whose business has been sold by his or her trustee without his or her concurrence, may both carry on a rival business and solicit his or her old customers.