Previously, an ondelete policy would be assigned to any required
Selection fields, the default policy being 'set null'.
Base fields do **not** require an ondelete value, since if they are
deleted there is no "data fix" to apply because the field's column is
dropped, and in fact it's error-prone to do so because during
`_process_ondelete`, the system would attempt to set to null fields that
were required (i.e. NOT NULL).
This issue is hidden by the fact that ir.model.fields are usually
deleted **before** ir.model.fields.selection and thus the ondelete
action won't be applied on the field with the original definition
(because it has probably been deleted by SQL CASCADE)
X-original-commit: 2e238f1e0202d65a98177939dac166dd659bb39c
Adrian Torres
75243d5a43