Getting the following regarly in my logs. The issue goes away when Sign artist is unloaded. 

I believe its a conflict between sign artist and bmgjets F1 spawn plugin. 

at ConVar.Admin.AdminUI_RequestFireworkPattern (ConsoleSystem+Arg arg) (at :0)
at ConsoleGen+<>c.<.cctor>b__2_205 (ConsoleSystem+Arg arg) (at :0)
at (wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.ConsoleSystem.Internal_Patch0(ConsoleSystem/Arg)
at UnityEngine.Debug:LogException(Exception)
at MonoMod.Utils.DynamicMethodDefinition:ConsoleSystem.Internal_Patch0(Arg)
at MonoMod.Utils.DynamicMethodDefinition:ConsoleSystem.Run_Patch1(Option, String, Object[])
at PlayerF1Spawn.ConsoleNetwork_OnClientCommand:Prefix(Message)
at MonoMod.Utils.DynamicMethodDefinition:ConsoleNetwork.OnClientCommand_Patch1(Message)
at ServerMgr:OnNetworkMessage(Message)
at Facepunch.Network.Raknet.Server:ProcessRead(NetRead)
at Network.BaseNetwork:Cycle()
at ServerMgr:Update()
NullReferenceException: Object reference not set to an instance of an object
at ConVar.Admin.AdminUI_RequestFireworkPattern (ConsoleSystem+Arg arg) [0x0006b] in :0
at ConsoleGen+<>c.<.cctor>b__2_205 (ConsoleSystem+Arg arg) [0x00000] in :0
at (wrapper dynamic-method) MonoMod.Utils.DynamicMethodDefinition.ConsoleSystem.Internal_Patch0(ConsoleSystem/Arg)
UnityEngine.DebugLogHandler:Internal_LogException(Exception, Object)
UnityEngine.DebugLogHandler:LogException(Exception, Object)
UnityEngine.Logger:LogException(Exception, Object)
UnityEngine.Debug:LogException(Exception)
MonoMod.Utils.DynamicMethodDefinition:ConsoleSystem.Internal_Patch0(Arg)
MonoMod.Utils.DynamicMethodDefinition:ConsoleSystem.Run_Patch1(Option, String, Object[])
PlayerF1Spawn.ConsoleNetwork_OnClientCommand:Prefix(Message)
MonoMod.Utils.DynamicMethodDefinition:ConsoleNetwork.OnClientCommand_Patch1(Message)
ServerMgr:OnNetworkMessage(Message)
Facepunch.Network.Raknet.Server:ProcessRead(NetRead)
Network.BaseNetwork:Cycle()
ServerMgr:Update()