`Field <field> doesn't have a default value` error when providing a table field mapping that matches the table's PK

[A-Baji]

Example:

- type: table
  input: A Id
  destination: test_group1_simple.TableA
  map:
    - type: attribute
      input: A Id
      destination: a_id

Or:

- type: table
  input: a_id
  destination: test_group1_simple.TableA

This is due to the map flattening step, where the table's PK mapping gets overwritten by the table's mapping due to them having the same key.