NullReferenceException at VehicleCache.GetFuelAmountFixed

NRE shows in console when I mount a row boat. I also get only the first NRE for mounting the RHIB. For both helis, Fuel values show correct upon mounting, but don't update during flight.

(11:25:39) | Failed to call hook 'OnEntityMounted' on plugin 'FuelGauge v0.5.1' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.FuelGauge+VehicleCache.GetFuelAmount () [0x0002a] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.CreateUI (Oxide.Plugins.FuelGauge+VehicleCache vehicle) [0x000a7] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.OnEntityMounted (BaseMountable entity, BasePlayer player) [0x000f5] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00279] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <d09a1f46ca2f4432811bcfe45ad13c7b>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <cf88a28c7fb44d36890d85a78331cc9d>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <cf88a28c7fb44d36890d85a78331cc9d>:0

(11:25:42) | Failed to run a 3.00 timer in 'FuelGauge v0.5.1' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.FuelGauge+VehicleCache.GetFuelAmount () [0x0002a] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.CreateUI (Oxide.Plugins.FuelGauge+VehicleCache vehicle) [0x000a7] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.UpdateUI (Oxide.Plugins.FuelGauge+VehicleCache vehicle) [0x00011] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Plugins.FuelGauge.<UIManager>m__0 () [0x0003a] in <04cb4053cd4e45b9a95fbf60d45c83e1>:0 
  at Oxide.Core.Libraries.Timer+TimerInstance.FireCallback () [0x00018] in <cf88a28c7fb44d36890d85a78331cc9d>:0
Locked automatically