Skipping Entity with id WitherSkull

Getting the following console error:

[10:47:51] [Server thread/WARN]: Skipping Entity with id WitherSkull
java.lang.NoSuchMethodException: ahu.<init>(aqs)
        at java.lang.Class.getConstructor0(Class.java:2810)
        at java.lang.Class.getConstructor(Class.java:1718)
        at xb.a(SourceFile:175)
        at bfw.a(SourceFile:330)
        at bfw.a(SourceFile:95)
        at bfw.a(SourceFile:83)
        at qs.e(SourceFile:129)
        at qs.c(SourceFile:81)
        at net.minecraft.server.MinecraftServer.k(SourceFile:315)
        at net.minecraft.server.MinecraftServer.a(SourceFile:286)
        at po.i(SourceFile:210)
        at net.minecraft.server.MinecraftServer.run(SourceFile:417)
        at java.lang.Thread.run(Thread.java:744)
[10:47:51] [Server thread/WARN]: Skipping Entity with id WitherSkull