[Error] Failed to call hook 'cmdAirstrike' on plugin 'Airstrike v0.3.6' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.Airstrike.cmdAirstrike (BasePlayer player, System.String command, System.String[] args) [0x00212] in <b3f4cb0cf846443e9c9d8c2a65465bb6>:0

  at Oxide.Plugins.Airstrike.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x005ed] in <b3f4cb0cf846443e9c9d8c2a65465bb6>: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

I also have this issue

[event] assets/prefabs/npc/cargo plane/cargo_plane.prefab
Failed to call hook 'isStrikePlane' on plugin 'Airstrike v0.3.6' (NullReferenceException: )
  at (wrapper managed-to-native) UnityEngine.Component.GetComponentFastPath(UnityEngine.Component,System.Type,intptr)
  at UnityEngine.Component.GetComponent[T] () [0x00021] in <fcaf289839f24125a059795f150fce14>:0 
  at Oxide.Plugins.Airstrike.isStrikePlane (CargoPlane plane) [0x00000] in <a2401a56a2444cddaf18eb651f29b051>:0 
  at Oxide.Plugins.Airstrike.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x004bb] in <a2401a56a2444cddaf18eb651f29b051>: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 
Exception while calling NextTick callback (InvalidCastException: Null object cannot be converted to a value type.)
  at System.Convert.ChangeType (System.Object value, System.Type conversionType, System.IFormatProvider provider) [0x00019] in <47fc8c70fa834cbf8141d7c1a7589125>:0 
  at System.Convert.ChangeType (System.Object value, System.Type conversionType) [0x00007] in <47fc8c70fa834cbf8141d7c1a7589125>:0 
  at Oxide.Core.Plugins.Plugin.Call[T] (System.String hook, System.Object[] args) [0x00008] in <18d4f19bbc844191b11ed9e69284d09b>:0 
  at Oxide.Plugins.MagicAirStrikePanel.IsStrikePlane (CargoPlane plane) [0x0000b] in <0751946dbe0047cdaab1f5a547ec2b61>:0 
  at Oxide.Plugins.MagicAirStrikePanel.CanShowPanel (CargoPlane plane) [0x00000] in <0751946dbe0047cdaab1f5a547ec2b61>:0 
  at Oxide.Plugins.MagicAirStrikePanel+<>c__DisplayClass13_0.<OnEntitySpawned>b__0 () [0x00000] in <0751946dbe0047cdaab1f5a547ec2b61>:0 
  at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <18d4f19bbc844191b11ed9e69284d09b>:0