Fix handling of list argument

Fix handling of list argument

I've learned that you cannot assign default values to a list
argument (something to do with mutability), so removing
the default value in the argument line and handling the case
where the keyword is called without passing in a list for
that argument.

Change-Id: I2b37e0c7a9a7708a234562541439de8db37eda84
Signed-off-by: Jamo Luhrsen <jluhrsen@redhat.com>