This section basically summarizes the list of things that could go wrong with the CommandAPI and how to mitigate these circumstances.

I encounter a NullPointerException when using Bukkit's scoreboard

Shove the scoreboard access inside a lambda, so it is evaluated when commands are executed rather than when the server loads. For example, use:

LinkedHashMap<String, Argument> arguments = new LinkedHashMap<>();
arguments.put("team", new TeamArgument().safeOverrideSuggestions(s ->
    Bukkit.getScoreboardManager().getMainScoreboard().getTeams().toArray(new Team[0]))

as opposed to:

LinkedHashMap<String, Argument> arguments = new LinkedHashMap<>();
arguments.put("team", new TeamArgument().safeOverrideSuggestions(
    Bukkit.getScoreboardManager().getMainScoreboard().getTeams().toArray(new Team[0]))

Server errors when loading datapacks in 1.16+

If you get an error at the very start of the server's startup sequence along the lines of:

[15:57:29] [Worker-Main-5/ERROR]: Failed to load function mycustomnamespace:test
java.util.concurrent.CompletionException: java.lang.IllegalArgumentException: Whilst parsing command on line 2: Unknown or incomplete command, see below for error at position 0: <--[HERE]
    at java.util.concurrent.CompletableFuture.encodeThrowable(Unknown Source) ~[?:1.8.0_261]
    at java.util.concurrent.CompletableFuture.completeThrowable(Unknown Source) [?:1.8.0_261]
    at java.util.concurrent.CompletableFuture$ Source) [?:1.8.0_261]
    at java.util.concurrent.CompletableFuture$AsyncSupply.exec(Unknown Source) [?:1.8.0_261]
    at java.util.concurrent.ForkJoinTask.doExec(Unknown Source) [?:1.8.0_261]
    at java.util.concurrent.ForkJoinPool$WorkQueue.runTask(Unknown Source) [?:1.8.0_261]
    at java.util.concurrent.ForkJoinPool.runWorker(Unknown Source) [?:1.8.0_261]
    at Source) [?:1.8.0_261]
Caused by: java.lang.IllegalArgumentException: Whilst parsing command on line 2: Unknown or incomplete command, see below for error at position 0: <--[HERE]
    at net.minecraft.server.v1_16_R1.CustomFunction.a(SourceFile:62) ~[spigot-1.16.1.jar:git-Spigot-758abbe-8dc1da1]
    at net.minecraft.server.v1_16_R1.CustomFunctionManager.a(SourceFile:84) ~[spigot-1.16.1.jar:git-Spigot-758abbe-8dc1da1]
    ... 6 more

You can safely ignore it - the CommandAPI fixes this later. This is described in more detail here.

Server/Plugin reloading

Due to the implementation of the CommandAPI, the CommandAPI does not support plugin reloading for plugins that use the CommandAPI. This includes, but is not limited to:

  • The /reload command which reloads all plugins on the server
  • Plugin reloading plugins, such as PlugMan
  • Any form of plugin enabling/disabling process for plugins which register commands via the CommandAPI

Developer's Note:

Plugin reloading gets very complicated with respect to the CommandAPI. Since the loading sequence of Minecraft commands is so picky, reloading the CommandAPI or a plugin which registers commands can cause commands to be re-registered. This can lead to very odd effects, such as command collisions (commands just don't work), to duplicate commands being registered under different namespaces (e.g. plugins are registered under Bukkit as well as Minecraft). These effects are not "100% guaranteed" and have only been seen during dodgy tests. In short, do not enable or reload plugins, and absolutely do not reload the server with /reload

Players cannot connect/timeout when joining

If players cannot connect, this could be due to the size of the command data packet. To see the resultant packet being sent to players when they log in, enable the create-dispatcher-json: true setting and view the file size of the resultant file. If the file size is abnormally large (Over 2MB is considered very large), consider reducing the number of LiteralArguments which your plugin uses.

Command conversion throws a NullPointerException

This is likely caused by the fact that the plugin you want to convert hasn't been loaded yet. Ensure that it loads before your plugin by adding the following to the target plugin's plugin.yml file:

loadbefore: [YourPlugin, CommandAPI]

My issue isn't on here, what do I do?!

If you've found a bug that isn't solved here, submit a bug report on the CommandAPI's issues page and I'll try my best to resolve the issue!