Description of problem:
Visit Virtualization -> Overview -> Migrations crashes the app.
It seems it won't crash if it's "No Datapoints found" in Bandwidth consumption, but if there are some data in Bandwidth consumption, the app is crashed.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. create a migratable VM
2. migrate the VM a few times
3. wait for some time and visit Virtualization -> Overview -> Migrations

Actual results:
the app crashed

Expected results:
it's okay to visit Virtualization -> Overview -> Migrations

Additional info: