Accept email without content as incoming document

It allow the creation of incoming document without data as long as it has
children. This supports the case of email without text nor HTML content but
only an attachment.

Closes #14109

modules/document_incoming/document.py

@@ -41,8 +41,11 @@ class Incoming(DeactivableMixin, Workflow, ModelSQL, ModelView):
     company = fields.Many2One('company.company', "Company", states=_states)
     data = fields.Binary(
         "Data", filename='name',
-        file_id=file_id, store_prefix=store_prefix, required=True,
-        states=_states)
+        file_id=file_id, store_prefix=store_prefix,
+        states={
+            'required': ~Eval('children'),
+            'readonly': _states['readonly'],
+            })
     parsed_data = fields.Dict(None, "Parsed Data", readonly=True)
     file_id = fields.Char("File ID", readonly=True)
     mime_type = fields.Function(
@@ -125,6 +128,14 @@ class Incoming(DeactivableMixin, Workflow, ModelSQL, ModelView):
                 },
             )
 
+    @classmethod
+    def __register__(cls, module):
+        super().__register__(module)
+        table_h = cls.__table_handler__(module)
+
+        # Migration from 7.6: remove not null on data
+        table_h.not_null_action('data', action='remove')
+
     @fields.depends('name')
     def on_change_with_mime_type(self, name=None):
         if self.name:

modules/document_incoming/tests/test_module.py

@@ -84,6 +84,35 @@ class DocumentIncomingTestCase(CompanyTestMixin, ModuleTestCase):
         self.assertEqual(child.data, b'data')
         self.assertEqual(child.source, 'inbound_email')
 
+    @with_transaction()
+    def test_document_from_inbound_email_without_content(self):
+        "Test document from inbound email without content"
+        pool = Pool()
+        Document = pool.get('document.incoming')
+        Email = pool.get('inbound.email')
+        Rule = pool.get('inbound.email.rule')
+
+        with patch.object(Email, 'as_dict') as as_dict:
+            as_dict.return_value = {
+                'subject': "Subject",
+                'attachments': [{
+                        'filename': "document",
+                        'data': b'data',
+                        }],
+                }
+
+            email = Email()
+            rule = Rule(
+                document_incoming_type='document_incoming',
+                document_incoming_company=None,
+                )
+
+            document = Document.from_inbound_email(email, rule)
+
+        self.assertFalse(document.data)
+        child, = document.children
+        self.assertEqual(child.data, b'data')
+
 
 class DocumentIncomingRouteTestCase(RouteTestCase):
     "Test Document Incoming route"