Apple has released a new version of iTunes for Mac with improved compatibility with the new Photos app.
iTunes 12.1.2 adds better support for syncing photos from Photos for Mac, released as part of OS X 10.10.3. You can see the complete set of changes below:
This update improves support for syncing photos to your iPhone, iPad, and iPod touch from the new Photos app for OS X. In addition, this update also adds several refinements to the Get Info window and improves overall stability.
Photos for Mac was recently released as part of OS X 10.10.3. You can grab iTunes 12.1.2 from the Updates section of the Mac App Store.