tasks: it's possible to update tasks/projects/labels to invalid states.

[saser]

For tasks and projects, it's possible to issue an Update{Task,Project} call that sets the title to the empty string, i.e., an Update{Task,Project}Request like:

task: {
    name: "tasks/1"
    title: "" # or just leaving it out
}
update_mask: {
    paths: ["title"]
}

The same goes for UpdateLabelRequest, but where the label field is set to the empty string.

There are currently no tests to catch this. Adding that should be the first step towards fixing this.