Revert "ContentRevisionRO: owner_id column must be not nullable"

tracim/migration/versions/da12239d9da0_delete_content_view.py

                     existing_type=sa.VARCHAR(length=32),
                     nullable=False,
                     server_default='')
-    op.alter_column('content_revisions', 'owner_id',
-                    existing_type=sa.INTEGER(),
-                    nullable=False)
     op.alter_column('content_revisions', 'status',
                     existing_type=sa.VARCHAR(length=32),
                     nullable=False,
     op.alter_column('content_revisions', 'revision_type',
                     existing_type=sa.VARCHAR(length=32),
                     nullable=True)
-    op.alter_column('content_revisions', 'owner_id',
-                    existing_type=sa.INTEGER(),
-                    nullable=True)
     op.alter_column('content_revisions', 'properties',
                     existing_type=sa.TEXT(),
                     nullable=True)

tracim/tracim/model/data.py

 
     revision_id = Column(Integer, primary_key=True)
     content_id = Column(Integer, ForeignKey('content.id'), nullable=False)
-    owner_id = Column(Integer, ForeignKey('users.user_id'), nullable=False)
+    owner_id = Column(Integer, ForeignKey('users.user_id'), nullable=True)
 
     label = Column(Unicode(1024), unique=False, nullable=False)
     description = Column(Text(), unique=False, nullable=False, default='')