#Bugs

## Not found entity
If a entity is not pressent in the Siren document is should set a (single) property to `null` instead of throwing an exception. Also add Mandatory attribute so this exception can be configured.
#Bugs

## Not found entity
If a entity is not pressent in the Siren document is should set a (single) property to `null` instead of throwing an exception. Also add Mandatory attribute so this exception can be configured.

# Features
- allow cancelation of requests (e.g. from the user, long upload, timeout..). See cancelation token.
Add new feature to todo
Add new feature to todo
