zfs list might list a bunch of transient snapshots if `zpool
listsnapshots=on` and something like zfs-auto-snapshot is used. It's
also not useful to graph them since they're unchanging in time, and
the parent volume is graphed anyway. Limit zfs list to
"filesystem,volume" instead of "all" including snapshots
> 2020/08/16 04:45:24 [ERROR] In RRD: Error updating /var/lib/munin/localdomain/localhost.localdomain-zfs_list_rpool__name-quota-g.rrd: /var/lib/munin/localdomain/localhost.localdomain-zfs_list_rpool__name-quota-g.rrd: Function update_pdp_prep, case DST_GAUGE - Cannot convert '-' to float
Used the correct munin way by soursing "$MUNIN_LIBDIR/plugins/plugin.sh" and use clean_fieldname.
For the title I removed the replacement of / by __ and on the multigraph value I added the usage of clean_fieldname to make it backwards compatible.