Unable to signup in erpnext

exc: “[“Traceback (most recent call last):\n File \“apps/frappe/frappe/app.py\”, line 65, in application\n response = frappe.handler.handle()\n File \“apps/frappe/frappe/handler.py\”, line 31, in handle\n data = execute_cmd(cmd)\n File \“apps/frappe/frappe/handler.py\”, line 68, in execute_cmd\n return frappe.call(method, **frappe.form_dict)\n File \“apps/frappe/frappe/init.py\”, line 1213, in call\n return fn(*args, **newargs)\n File \“apps/frappe/frappe/core/doctype/user/user.py\”, line 778, in sign_up\n user.insert()\n File \“apps/frappe/frappe/model/document.py\”, line 270, in insert\n self.run_post_save_methods()\n File \“apps/frappe/frappe/model/document.py\”, line 1008, in run_post_save_methods\n self.run_method(\“on_update\”)\n File \“apps/frappe/frappe/model/document.py\”, line 873, in run_method\n out = Document.hook(fn)(self, *args, **kwargs)\n File \“apps/frappe/frappe/model/document.py\”, line 1165, in composer\n return composed(self, method, *args, **kwargs)\n File \“apps/frappe/frappe/model/document.py\”, line 1148, in runner\n add_to_return_value(self, fn(self, *args, **kwargs))\n File \“apps/frappe/frappe/model/document.py\”, line 870, in fn\n return method_object(*args, **kwargs)\n File \“apps/frappe/frappe/core/doctype/user/user.py\”, line 112, in on_update\n self.send_password_notification(self.__new_password)\n File \“apps/frappe/frappe/core/doctype/user/user.py\”, line 252, in send_password_notification\n self.send_welcome_mail_to_user()\n File \“apps/frappe/frappe/core/doctype/user/user.py\”, line 315, in send_welcome_mail_to_user\n self.send_login_mail(subject, \“new_user\”,\n File \“apps/frappe/frappe/core/doctype/user/user.py\”, line 342, in send_login_mail\n frappe.sendmail(recipients=self.email, sender=sender, subject=subject,\n File \“apps/frappe/frappe/init.py\”, line 553, in sendmail\n queue.send(recipients=recipients, sender=sender,\n File \“apps/frappe/frappe/email/queue.py\”, line 79, in send\n sender = email_account.default_sender\nAttributeError: ‘NoneType’ object has no attribute ‘default_sender’\n”]”
exception: “AttributeError: ‘NoneType’ object has no attribute ‘default_sender’”