Erros skip nil in Add function

[knqyf263]

Make sure these boxes checked before submitting your pull request.

• Do only one thing
• No API-breaking changes
• New code/logic commented & tested
• Write good commit message, try to squash your commits into a single one
• Run ./build.sh in gh-pages branch for document changes

For significant changes like big bug fixes, new features, please open an issue to make a agreement on an implementation design/plan first before starting it.

Thank you.

What did this pull request do?

To skip nil in Add .

I wrote the following code.

conn *gorm.DB
...
tx := conn.Begin()
var errs gorm.Errors
errs = errs.Add(tx.Delete(&foo).Error)
errs = errs.Add(tx.Delete(&bar).Error)

if errs.Error() != "" {
  tx.Rollback()
  return
}
...

I got the error.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x43e6f75]

I checked errs variable.

gorm.Errors{
  nil,
}

I think Errors doesn't need to have nil.
Or should I always write like this?

if err := tx.Delete(&foo).Error; err != nil {
  errs = errs.Add(err)
}

Is not it supposed that nil will be added?

Thanks!

[jinzhu]

thank you for your PR.