The good news is that Appleseed still works in 1.13, except for sign posting. The sign feature is broken and the following error appears whenever a sign is placed anyway.
[21:07:33] [Server thread/ERROR]: Could not pass event SignChangeEvent to Appleseed v0.7.6-b26 org.bukkit.event.EventException: null at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:308) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:500) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:485) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PlayerConnection.a(PlayerConnection.java:2377) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PacketPlayInUpdateSign.a(SourceFile:44) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PacketPlayInUpdateSign.a(SourceFile:10) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PlayerConnectionUtils.a(SourceFile:10) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_181] at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_181] at net.minecraft.server.v1_13_R1.SystemUtils.a(SourceFile:198) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.w(MinecraftServer.java:884) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.DedicatedServer.w(DedicatedServer.java:411) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.v(MinecraftServer.java:819) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.run(MinecraftServer.java:717) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_181] Caused by: java.lang.NoSuchMethodError: org.bukkit.craftbukkit.v1_13_R1.util.CraftEvil.getType(Lorg/bukkit/block/Sign;)Lorg/bukkit/Material; at redsgreens.Appleseed.AppleseedBlockListener.getBlockBehindWallSign(AppleseedBlockListener.java:123) ~[?:?] at redsgreens.Appleseed.AppleseedBlockListener.onSignChange(AppleseedBlockListener.java:36) ~[?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:304) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] ... 15 more
The good news is that Appleseed still works in 1.13, except for sign posting. The sign feature is broken and the following error appears whenever a sign is placed anyway.
[21:07:33] [Server thread/ERROR]: Could not pass event SignChangeEvent to Appleseed v0.7.6-b26 org.bukkit.event.EventException: null at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:308) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:500) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:485) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PlayerConnection.a(PlayerConnection.java:2377) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PacketPlayInUpdateSign.a(SourceFile:44) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PacketPlayInUpdateSign.a(SourceFile:10) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.PlayerConnectionUtils.a(SourceFile:10) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511) [?:1.8.0_181] at java.util.concurrent.FutureTask.run(FutureTask.java:266) [?:1.8.0_181] at net.minecraft.server.v1_13_R1.SystemUtils.a(SourceFile:198) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.w(MinecraftServer.java:884) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.DedicatedServer.w(DedicatedServer.java:411) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.v(MinecraftServer.java:819) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at net.minecraft.server.v1_13_R1.MinecraftServer.run(MinecraftServer.java:717) [spigot-1.13.jar:git-Spigot-69774b3-a9c796f] at java.lang.Thread.run(Thread.java:748) [?:1.8.0_181] Caused by: java.lang.NoSuchMethodError: org.bukkit.craftbukkit.v1_13_R1.util.CraftEvil.getType(Lorg/bukkit/block/Sign;)Lorg/bukkit/Material; at redsgreens.Appleseed.AppleseedBlockListener.getBlockBehindWallSign(AppleseedBlockListener.java:123) ~[?:?] at redsgreens.Appleseed.AppleseedBlockListener.onSignChange(AppleseedBlockListener.java:36) ~[?:?] at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_181] at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_181] at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_181] at java.lang.reflect.Method.invoke(Method.java:498) ~[?:1.8.0_181] at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:304) ~[spigot-1.13.jar:git-Spigot-69774b3-a9c796f] ... 15 more