error on upgrade to 5.3
I posted this to gitlab here https://lab.civicrm.org/dev/core/issues/250 and the issue turned out to be related to odd records in my database. 

this query, from Elieen exposed the bad row

SELECT p.id, p.name, p.class_name, p.is_active, pt.id, pt.class_name, pt.name
FROM civicrm_payment_processor p
LEFT JOIN civicrm_payment_processor_type pt ON pt.id = p.payment_processor_type_id
+----+--------------------+----------------------+-----------+------+----------------------+---------+
| id | name               | class_name           | is_active | id   | class_name           | name    |
+----+--------------------+----------------------+-----------+------+----------------------+---------+
|  1 | Dummy Processor    | Payment_PayPalImpl   |         1 |   10 | Payment_Dummy        | Dummy   |
|  2 | Dummy Processor    | Payment_Dummy        |         1 |   10 | Payment_Dummy        | Dummy   |


so I updated the row in civicrm_payment_processor to change Payment_PayPalImpl to Payment_Dummy and everything works without the modification to civi code.