- please see attached image and video in comments

How we can reproduce it using the example you attached
1 Create new project
2 Go to Project view and create new "Animator Controller"(Right Mouse click -> Create->Animator Controller) and open it
3 in "Animator" view create new Blend Tree and open it (double click on it)
4 Select Blend Tree

Actual results:
The numbers in Preview window (in Inspector) are "- Infinity" (-2147483648:52), and also you allowed to press Play button

Expected results:
The numbers in Preview window shouldn't be "- Infinity", maybe just "0" or "null". And think that Play button could be disabled as it is nothing to play