When i set serwerrewards to true i can not buy boats

(08:30:15) | Failed to call hook 'CmdBuyBoat' on plugin 'BoatLicence v0.6.3' (InvalidCastException: Null object cannot be converted to a value type.)
  at System.Convert.ChangeType (System.Object value, System.Type conversionType, System.IFormatProvider provider) [0x00029] in <e1a80661d61443feb3dbdaac88eeb776>:0 
  at System.Convert.ChangeType (System.Object value, System.Type conversionType) [0x0000c] in <e1a80661d61443feb3dbdaac88eeb776>:0 
  at Oxide.Core.Plugins.Plugin.Call[T] (System.String hook, System.Object[] args) [0x00008] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Plugins.BoatLicence.CmdBuyBoat (BasePlayer player, System.String command, System.String[] args) [0x0050d] in <43a5d6262f07467a8b164ef28ffa941e>:0 
  at Oxide.Plugins.BoatLicence.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x0038d] in <43a5d6262f07467a8b164ef28ffa941e>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

{
  "Can buy RHIB": true,
  "Can buy rowing boat": true,
  "Cooldown time in seconds to use the chat command to spawn a boat": 60,
  "Cost of RHIB": 100000,
  "Cost of rowing boat": 100000,
  "Interval in minutes to check boat for wipe": 5,
  "Shortname of item needed to buy boat": "scrap",
  "Time before boat wipe in minutes": 15,
  "Use Economics to buy boat": false,
  "Use ServerRewards to buy boat": true
}

i have the same issue as Ryrzy i've updated to 1.1.0 and still get it

Failed to call hook 'CmdBuyVehicle' on plugin 'VehicleLicence v1.1.0' (InvalidCastException: Null object cannot be converted to a value type.)
  at System.Convert.ChangeType (System.Object value, System.Type conversionType, System.IFormatProvider provider) [0x00029] in :0
  at System.Convert.ChangeType (System.Object value, System.Type conversionType) [0x0000c] in :0
  at Oxide.Core.Plugins.Plugin.Call[T] (System.String hook, System.Object[] args) [0x00008] in <4452f821def6406d834e4149849fe7ea>:0
  at Oxide.Plugins.VehicleLicence.Withdraw (BasePlayer player, Oxide.Plugins.VehicleLicence+VehicleSettings vehicleSettings) [0x000a3] in :0
  at Oxide.Plugins.VehicleLicence.BuyVehicle (BasePlayer player, Oxide.Plugins.VehicleLicence+LicencedPlayer licencedPlayer, System.String prefab) [0x00069] in :0
  at Oxide.Plugins.VehicleLicence.CmdBuyVehicle (BasePlayer player, System.String command, System.String[] args) [0x00195] in :0
  at Oxide.Plugins.VehicleLicence.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x003d2] in :0
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

here is my Current config:
{
"Define your licence settings": {
"Interval in minutes to check vehicle for wipe": 10,
"Time before vehicle wipe in minutes": 30,
"Use Economics to buy vehicles": false,
"Use ServerRewars to buy vehicles": true,
"Shortname of item needed to buy vehicles": "scrap",
"Use permissions for chat commands": false
},