Enforce at least one parameter in CommandManager#register()

The old register method has been deprecated.

api/src/main/java/com/velocitypowered/api/command/CommandManager.java

@@ -10,9 +10,22 @@ public interface CommandManager {
    *
    * @param command the command to register
    * @param aliases the alias to use
+   *
+   * @deprecated This method requires at least one alias, but this is only enforced at runtime.
+   *             Prefer {@link #register(String, Command, String...)} instead.
    */
+  @Deprecated
   void register(Command command, String... aliases);
 
+  /**
+   * Registers the specified command with the manager with the specified aliases.
+   *
+   * @param alias the first alias to register
+   * @param command the command to register
+   * @param otherAliases the other aliases to use
+   */
+  void register(String alias, Command command, String... otherAliases);
+
   /**
    * Unregisters a command.
    *

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -167,10 +167,10 @@ public class VelocityServer implements ProxyServer {
     cm.logChannelInformation();
 
     // Initialize commands first
-    commandManager.register(new VelocityCommand(this), "velocity");
-    commandManager.register(new ServerCommand(this), "server");
-    commandManager.register(new ShutdownCommand(this), "shutdown", "end");
-    commandManager.register(new GlistCommand(this), "glist");
+    commandManager.register("velocity", new VelocityCommand(this));
+    commandManager.register("server", new ServerCommand(this));
+    commandManager.register("shutdown", new ShutdownCommand(this),"end");
+    commandManager.register("glist", new GlistCommand(this));
 
     try {
       Path configPath = Paths.get("velocity.toml");

proxy/src/main/java/com/velocitypowered/proxy/command/VelocityCommandManager.java

@@ -7,27 +7,35 @@ import com.velocitypowered.api.command.Command;
 import com.velocitypowered.api.command.CommandManager;
 import com.velocitypowered.api.command.CommandSource;
 import com.velocitypowered.api.command.RawCommand;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
-import org.checkerframework.checker.nullness.qual.NonNull;
 
 public class VelocityCommandManager implements CommandManager {
 
   private final Map<String, Command> commands = new HashMap<>();
 
   @Override
+  @Deprecated
   public void register(final Command command, final String... aliases) {
-    Preconditions.checkNotNull(aliases, "aliases");
+    Preconditions.checkArgument(aliases.length > 0, "no aliases provided");
+    register(aliases[0], command, Arrays.copyOfRange(aliases, 1, aliases.length));
+  }
+
+  @Override
+  public void register(String alias, Command command, String... otherAliases) {
+    Preconditions.checkNotNull(alias, "alias");
+    Preconditions.checkNotNull(otherAliases, "otherAliases");
     Preconditions.checkNotNull(command, "executor");
-    for (int i = 0, length = aliases.length; i < length; i++) {
-      final String alias = aliases[i];
-      Preconditions.checkNotNull(alias, "alias at index %s", i);
-      this.commands.put(alias.toLowerCase(Locale.ENGLISH), command);
+    this.commands.put(alias.toLowerCase(Locale.ENGLISH), command);
+
+    for (int i = 0, length = otherAliases.length; i < length; i++) {
+      final String alias1 = otherAliases[i];
+      Preconditions.checkNotNull(alias1, "alias at index %s", i + 1);
+      this.commands.put(alias1.toLowerCase(Locale.ENGLISH), command);
     }
   }