it would be of great help if the "one minute" restriction as well as the string restriction were a comment in the rrd4j.persist file (see below).
Finally it is not clear if Switch or Contact items can be stored or not.
I would be happy if you could add this to the repository so that the demo files will include this hint in the future.
// persistence strategies have a name and a definition and are referred to in the "Items" section
// for rrd charts, we need a cron strategy of one minute (mandatory to make rrd charts work)
everyMinute : "0 * * * * ?"
// storable items have to be of type Number
// rrd does not store strings !!!
DemoSwitch,NoOfLights,Window_GF_Toilet,Heating* : strategy = everyChange, everyMinute, restoreOnStartup
// let's only store temperature values in rrd
Temperature*,Weather_Chart* : strategy = everyMinute, restoreOnStartup