covariate_table: Avoid copying unused key space when packing
covariate_table: Avoid copying unused key space when packing

NVlabs/firepony,NVlabs/firepony,broadinstitute/firepony,broadinstitute/firepony,broadinstitute/firepony,broadinstitute/firepony,NVlabs/firepony,NVlabs/firepony