perf: Decrease time to create a claim by ~1 us

A simple change to the way kwargs was constructed made a signficant
change in efficiency. Other places where the helpers.purge function
are used will be optimized once Falcon releases support for storing
results directly in a dict, unless they are None, making the purge
function unnecessary.

Implements: Blueprint bp/v1-obvious-optimizations
Change-Id: I9abe4d497cedd7963ae0cccd85bc1096d20994a1