Default value migration

[fishead]

Great project.

Default value of string like field can be empty string "" or "null", So why check it like this?

atlas/sql/internal/sqlx/sqlx.go

Lines 18 to 21 in 787354f

	// ValidString reports if the given string is not null and valid.
	func ValidString(s sql.NullString) bool {
	return s.Valid && s.String != "" && strings.ToLower(s.String) != "null"
	}

I'm not an expert of this, any special consideration?

edit:
After test with my own project and as @a8m mentioned in comment, the function is not the problem.

[a8m]

Hey @fishead 👋

It should be fixed. Let me know if you want to contribute and I can guide you, or I can do it later today 🙏

[fishead]

I'm glad to make a PR.

[a8m]

Here's where we handle the default values:
https://github.com/ariga/atlas/blob/master/sql/mysql/inspect.go#L240
https://github.com/ariga/atlas/blob/master/sql/postgres/inspect.go#L181
https://github.com/ariga/atlas/blob/master/sql/sqlite/inspect.go#L141

We should use defaults.Valid instead of sqlx.ValidString. Just note that I added a commit (sqltest) in #622 to fix testing for it, so rebase and it's merged.

[fishead]

@a8m patch is here #626, just let me known if it's not appropriate.
You are so friendly in the ent community.

[a8m]

Fixed with #626. Thanks a lot @fishead