[Observium] bind application cache graphics problem

Hello!

My bind_cache graph has -nan values. It was normal before.

RRD CMD[update /opt/observium/rrd/hostxyz/app-bind-4-cache-default.rrd N:9:1:::16205:85:1052:1594:45:9:1311::17355:2:::71:8::5:13:13:::::::363::1254::6184::1754::::::1307:4367::::::] RRD RUNTIME[0.0011s] RRD STDOUT[ERROR: /opt/observium/rrd/hostxyz/app-bind-4-cache-default.rrd: Function update_pdp_prep, case DST_GAUGE - Cannot convert '' to float] RRD_STATUS[FALSE]

How can I fix this ?