Undefined array key 0 when sending offline event receipt
It seems to be $lineItem[0] at https://github.com/civicrm/civicrm-core/blob/44efaf52507df2445908e02c30caef62ada0100a/CRM/Event/Form/Participant.php#L1353. It looks like it might not always be defined if editing an existing participant. But it's also confusing because it looks like sometimes it will be 0 and sometimes the array is keyed on price set id.