/usr/lib/lua/luci/dispatcher.lua:448: Failed to execute call dispatcher target for entry '/admin/statistics/graph/load'.
The called action terminated with an exception:
/usr/lib/lua/luci/util.lua:209: attempt to get length of local 'str' (a nil value)
stack traceback:
  [C]: in function 'assert'
  /usr/lib/lua/luci/dispatcher.lua:448: in function 'dispatch'
  /usr/lib/lua/luci/dispatcher.lua:195: in function </usr/lib/lua/luci/dispatcher.lua:194>