can't initialize from 'dict' without generators

Raise code

ethod
    def _from_dict(cls, rep, opt):
        """Construct a polynomial from a ``dict``. """
        gens = opt.gens

        if not gens:
            raise GeneratorsNeeded(
                "can't initialize from 'dict' without generators")

        level = len(gens) - 1
        domain = opt.domain

        if domain is None:
            domain, rep = construct_domain(rep, opt=opt)
        else