Comment 2 for bug 1131418

Actually, looking at the code, the tag definition should be a valid expression otherwise you would have gotten an error when the tag was created. That's why I now suspect that you have non-valid hardware info (created by lshw).

Here is out to print the hardware info recorded by lshw:
# start python shell
sudo maas shell
# in python shell:
>>> from maasserver.models import Node
>>> [node.hardware_details for node in Node.objects.all()]