Players are unable to purchase any items/commands in the shop, and get this error when trying to do so. 

04:56 [Error] Failed to call hook 'cmdBuyCommand' on plugin 'ServerRewards v0.4.73' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.ServerRewards.cmdBuyCommand (ConsoleSystem+Arg arg) [0x00057] in <1859cbefb3f74aaf914ed16132c4e0b5>:0 
  at Oxide.Plugins.ServerRewards.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00e2a] in <1859cbefb3f74aaf914ed16132c4e0b5>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <09575a60985045248bcb43b20faeeb99>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <bae5f1223fce49c493b01571c99dce02>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <bae5f1223fce49c493b01571c99dce02>:0 ​

Any solutions? Already tried wiping config and data.