jenseng/immigrant — pull request #16 by eturino (2014-09-19 13:23:07+00:00)
Title: add_key migration: exclude abstract classes -> FKs without table

If a relationship is defined in an abstract class, the FK is created with `nil` on `from_table` or `to_table`. This provokes a no method error on nil class.

In order to avoid that, we can exclude from the FKs list any FK with a missing table.