Undefined index: payment_type
On dmaster I changed default contribution page to purchase memberships so it allowed pay later, went to live page and did a pay later payment for a $100 membership and got (on https://dmaster.demo.civicrm.org/civicrm/contribute/transact?_qf_Confirm_display=true&qfKey=CRMContributeControllerContribution4dhfkffigym8c4c8k0kos0ko00440gkg8008wss00gowwc8ckw_9868): Notice: Undefined index: payment_type in CRM_Core_Payment->validatePaymentInstrument() (line 511 of /srv/buildkit/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/Payment.php).
Dummy Payment processor is only defined payment processor and it is enabled.
Changing Fall Fundraising default event to allow Pay Later, then using Live page to do so, also results in an error on the confirm but not Thank You page (https://dmaster.demo.civicrm.org/civicrm/event/register?_qf_Confirm_display=true&qfKey=CRMEventControllerRegistrationxabxsqxsysgg88scss808ksog0o4okko84cw4ok0s0ss8cgsk_1767): Notice: Undefined index: payment_type in CRM_Core_Payment->validatePaymentInstrument() (line 511 of /srv/buildkit/build/dmaster/web/sites/all/modules/civicrm/CRM/Core/Payment.php).