Create todos for epics
Summary
We have project
validation and NOT NULL
constraint on Todo
. That doesn't allow us to create todos for objects without project. So far I am aware of at least personal snippets (no project, no group) and epics (parent is group) will have that problem too.
Suggestion
Remove the project constraint and validate only when the object belong to a project. Create todos for mentioned users on epics
Note
Creating todos from Issuables UpdateService
could be extracted to another class - we have quite a lot of code duplication there.