Source:
public Optional<CommandMapping> register(Object plugin, CommandCallable callable, List<String> aliases, Function<List<String>, List<String>> callback) { checkNotNull(plugin, "plugin"); Optional<PluginContainer> containerOptional = Sponge.getGame().getPluginManager().fromInstance(plugin); if (!containerOptional.isPresent()) { throw new IllegalArgumentException( "The provided plugin object does not have an associated plugin container " + "(in other words, is 'plugin' actually your plugin object?"); } PluginContainer container = containerOptional.get(); synchronized (this.lock) { List<String> aliasesWithPrefix = new ArrayList<>(aliases.size() * 3); for (String alias : aliases) { if (alias.contains(" ")) { throw new IllegalArgumentException("Plugin " + container.getId() + " attempted to register an invalid alias ('" + alias + "'). Aliases may not contain spaces."); } final Collection<CommandMapping> ownedCommands = this.owners.get(container); for (CommandMapping mapping : this.dispatcher.getAll(alias)) { if (ownedCommands.contains(mapping)) { boolean isWrapper = callable instanceof MinecraftCommandWrapper; if (!(isWrapper && ((MinecraftCommandWrapper) callable).suppressDuplicateAlias(alias))) { throw new IllegalArgumentException("A plugin may not register multiple commands for the same alias ('" + alias + "')!"); } } } aliasesWithPrefix.add(alias); aliasesWithPrefix.add(container.getId() + ':' + alias); } Optional<CommandMapping> mapping = this.dispatcher.register(callable, aliasesWithPrefix, callback); if (mapping.isPresent()) { this.owners.put(container, mapping.get()); this.reverseOwners.put(mapping.get(), container); } return mapping; } }

Target:
public Optional<CommandMapping> register(Object plugin, CommandCallable callable, List<String> aliases, Function<List<String>, List<String>> callback) { checkNotNull(plugin, "plugin"); Optional<PluginContainer> containerOptional = Sponge.getGame().getPluginManager().fromInstance(plugin); if (!containerOptional.isPresent()) { throw new IllegalArgumentException( "The provided plugin object does not have an associated plugin container " + "(in other words, is 'plugin' actually your plugin object?"); } PluginContainer container = containerOptional.get(); synchronized (this.lock) { List<String> aliasesWithPrefix = new ArrayList<>(aliases.size() * 3); for (String alias : aliases) { if (alias.contains(" ")) { throw new IllegalArgumentException("Plugin '" + container.getId() + "' attempted to register an alias ('" + alias + "') which contained a space."); } final Collection<CommandMapping> ownedCommands = this.owners.get(container); for (CommandMapping mapping : this.dispatcher.getAll(alias)) { if (ownedCommands.contains(mapping)) { boolean isWrapper = callable instanceof MinecraftCommandWrapper; if (!(isWrapper && ((MinecraftCommandWrapper) callable).suppressDuplicateAlias(alias))) { throw new IllegalArgumentException("A plugin may not register multiple commands for the same alias ('" + alias + "')!"); } } } aliasesWithPrefix.add(alias); aliasesWithPrefix.add(container.getId() + ':' + alias); } Optional<CommandMapping> mapping = this.dispatcher.register(callable, aliasesWithPrefix, callback); if (mapping.isPresent()) { this.owners.put(container, mapping.get()); this.reverseOwners.put(mapping.get(), container); } return mapping; } }