Custom map button gives me errors.

Failed to call hook 'cmdCustomMaps' on plugin 'MapVoter v1.1.19' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.MapVoter.TGetImage (System.String name, System.UInt64 skinId) [0x0000b] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.MapVoter.CreateCustomMapSelectEntry (BasePlayer player, Oxide.Game.Rust.Cui.CuiElementContainer container, Oxide.Plugins.MapVoter+CustomMap map, System.Int32 index, System.Int32 page, System.UInt64 npcId) [0x0000e] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.MapVoter.CreateCustomMapSelectView (BasePlayer player, Oxide.Game.Rust.Cui.CuiElementContainer container, System.Int32 page, System.UInt64 npcId) [0x0006d] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.MapVoter.OpenCustomMapSelect (BasePlayer player, System.Int32 page, System.Boolean overwrite) [0x00122] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.MapVoter.cmdCustomMaps (Oxide.Core.Libraries.Covalence.IPlayer player, System.String cmd, System.String[] args) [0x0003a] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.MapVoter.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x01113] in <bcb230e5be9f4b05bb7eddfe1d72fa6f>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <87ce9ac9776a48658bc55eae6debe38b>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <18d4f19bbc844191b11ed9e69284d09b>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <18d4f19bbc844191b11ed9e69284d09b>:0