asPercent: don't panic on empty input
asPercent: don't panic on empty input

raintank/metrictank,replay/metrictank,raintank/metrictank,raintank/raintank-metric,raintank/raintank-metric,raintank/metrictank,replay/metrictank,replay/metrictank,replay/metrictank,raintank/raintank-metric,raintank/metrictank