Missing 'full' display causes Fatal error: Unsupported operand types in modules/field/field.crud.inc line 598

The full display on one field out of 40 on my D6->D7 upgrade project is missing. content_migrate.module assumes it is available which causes an error during batch migration:

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /batch?id=179&op=do
StatusText: OK
ResponseText: 
( ! ) Fatal error: Unsupported operand types in /home/user/public_html/modules/field/field.crud.inc on line 598
Call Stack
#TimeMemoryFunctionLocation
10.0001653568{main}(  )../index.php:0
20.204235797152menu_execute_active_handler(  )../index.php:21
30.211537164472call_user_func_array
(  )../menu.inc:517
40.211537164840system_batch_page(  )../menu.inc:0
50.211537164840_batch_page(  )../system.admin.inc:2333
60.211537166216_batch_do(  )../batch.inc:80
70.211537166216_batch_process(  )../batch.inc:161
80.214037504040call_user_func_array
(  )../batch.inc:284
90.214037504104_content_migrate_batch_process_create_fields(  )../batch.inc:0
100.673956899608field_create_instance(  )../content_migrate.admin.inc:257
110.676556913384_field_write_instance(  )../field.crud.inc:493

Solution is to check that the full display exists. Patched attached.