def get_subs_dict(self, qnodes=None):
        """
        Return substitution dict for replacements into the template
        Subclasses may want to customize this method.
        """
        #d = self.qparams.copy()
        d = self.qparams
        d.update(self.optimize_params(qnodes=qnodes))
        # clean null values
        subs_dict = {k: v for k, v in d.items() if v is not None}
        #print("subs_dict:", subs_dict)
        return subs_dict