text: Title: Asynchronous Graphs results in a empty graph if the unit are kWh.
  Body:  Asynchronous Graphs from  kWh results in a empty graph.
  
   - From Mycodo Version: 8.15.1
   - Raspberry Pi Version: 3B+
   - Raspbian OS Version: Raspberry pi os(64-bit)
  
  I had version 8.14.2 running, to my great satisfaction, one of the inputs measures the electricity consumption (kWh).
  I've found that since the update to version 8.15.1 Asynchronous Graphs from  the electricity consumption results in a empty graph.
  I've changed the units of this input ,  from kWh to Angle(degrees), and the historical measurements reappear.
  With the update to version 8.15.4, i had adjusted the units back from(Angle to kWh), and it didn't work again.
  
  