Vaadin Flow 1.2.1 is a maintenance version with the following notable changes:

Security fixes

• Return back preventing disallowed property update (#4774) (#4778)
  -> Please update your Vaadin platform version to 12.0.0 (available 4th December 2018) or newer to get the Flow version 1.2.1 with security fix included. For Vaadin 10 and 11 (Flow 1.0), the fix is included in 10.0.8 and 11.0.3.

Bug fixes

• Only print warnings for the first time we check the properties. (#4766)
• Handle tree modifications inside attach/detach listeners (#4787), fixes #4209

See complete list of changes since previous version