Make `Attributes.ToV2` method to return `nil`
when called on `nil`. Make `NewAttributesFromV2`
function to return `nil` when called on `nil`.
Write corresponding unit tests.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
Document field values of instance constructed via `NewAttribute`.
Assert the values in corresponding unit test.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
Document that `Attribute.ToV2` method returns
`nil` when is called on `nil`. Add
corresponding unit test.
Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>
