Skeleton spawn not working

[Dream3rz]

This shows up in SMAPI [game] An error occurred in the base update loop: System.MissingMethodException: Constructor on type 'StardewValley.Monsters.Skeleton' not found. at System.RuntimeType.CreateInstanceImpl(BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes, StackCrawlMark& stackMark) at System.Activator.CreateInstance(Type type, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes) at System.Activator.CreateInstance(Type type, Object[] args) at Spawn_Monsters.MonsterSpawning.Spawner.SpawnMonster(Monster monster, Vector2 location) in E:\Programming\GitHub\SpawnMonsters\Spawn Monsters\MonsterSpawning\Spawner.cs:line 61 at Spawn_Monsters.MonsterPlaceMenu.receiveLeftClick(Int32 x, Int32 y, Boolean playSound) in E:\Programming\GitHub\SpawnMonsters\Spawn Monsters\MonsterMenu\MonsterPlaceMenu.cs:line 53 at StardewValley.Game1.updateActiveMenu(GameTime gameTime) in C:\GitlabRunner\builds\Gq5qA5P4\1\ConcernedApe\stardewvalley\Farmer\Farmer\Game1.cs:line 5240 at StardewValley.Game1._update(GameTime gameTime) in C:\GitlabRunner\builds\Gq5qA5P4\1\ConcernedApe\stardewvalley\Farmer\Farmer\Game1.cs:line 4574 at StardewValley.Game1.Update(GameTime gameTime) in C:\GitlabRunner\builds\Gq5qA5P4\1\ConcernedApe\stardewvalley\Farmer\Farmer\Game1.cs:line 3757 at StardewModdingAPI.Framework.SGame.<>c__DisplayClass35_0.b__0() in C:\source_Stardew\SMAPI\src\SMAPI\Framework\SGame.cs:line 169 at StardewModdingAPI.Framework.SCore.OnPlayerInstanceUpdating(SGame instance, GameTime gameTime, Action runUpdate) in C:\source_Stardew\SMAPI\src\SMAPI\Framework\SCore.cs:line 987