Fix some regression on command flag registering and completion

src/main/java/com/onarandombox/MultiverseCore/commandtools/MVCommandCompletions.java

@@ -21,6 +21,7 @@ import com.onarandombox.MultiverseCore.api.MVWorldManager;
 import com.onarandombox.MultiverseCore.config.MVCoreConfig;
 import com.onarandombox.MultiverseCore.destination.DestinationsProvider;
 import com.onarandombox.MultiverseCore.destination.ParsedDestination;
+import io.vavr.control.Try;
 import jakarta.inject.Inject;
 import org.bukkit.GameRule;
 import org.jetbrains.annotations.NotNull;
@@ -95,8 +96,11 @@ public class MVCommandCompletions extends PaperCommandCompletions {
     }
 
     private Collection<String> suggestFlags(@NotNull BukkitCommandCompletionContext context) {
-        return this.commandManager.getFlagsManager().suggest(
-                context.getConfig("groupName", ""), context.getContextValue(String[].class));
+        String groupName = context.getConfig("groupName", "");
+
+        return Try.of(() -> context.getContextValue(String[].class))
+                .map(flags -> commandManager.getFlagsManager().suggest(groupName, flags))
+                .getOrElse(Collections.emptyList());
     }
 
     private Collection<String> suggestGamerules() {

src/main/java/com/onarandombox/MultiverseCore/commandtools/MultiverseCommand.java

@@ -11,7 +11,7 @@ import org.jetbrains.annotations.NotNull;
 import org.jvnet.hk2.annotations.Contract;
 
 @Contract
-public abstract class MultiverseCommand extends BaseCommand {
+public abstract class  MultiverseCommand extends BaseCommand {
 
     protected final MVCommandManager commandManager;
     private String flagGroupName;
@@ -33,11 +33,12 @@ public abstract class MultiverseCommand extends BaseCommand {
         return commandManager.getFlagsManager();
     }
 
-    protected CommandFlag flag(CommandFlag flag) {
+    protected <T extends CommandFlag> T flag(T flag) {
         if (flagGroupBuilder == null) {
             flagGroupBuilder = CommandFlagGroup.builder("mv" + getClass().getSimpleName().toLowerCase());
         }
         flagGroupBuilder.add(flag);
+        Logging.finest("Registered flag: " + flag);
         return flag;
     }
 

src/main/java/com/onarandombox/MultiverseCore/commandtools/flags/CommandFlag.java

@@ -52,6 +52,17 @@ public class CommandFlag {
         return aliases;
     }
 
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    public String toString() {
+        return "Builder{"
+                + "key='" + key + '\''
+                + ", aliases=" + aliases
+                + '}';
+    }
+
     /**
      * A builder for a flag.
      *

src/main/java/com/onarandombox/MultiverseCore/commandtools/flags/CommandValueFlag.java

@@ -191,7 +191,7 @@ public class CommandValueFlag<T> extends CommandFlag {
          * @return The flag.
          */
         @Override
-        public @NotNull CommandFlag build() {
+        public @NotNull CommandValueFlag<T> build() {
             if (context == null && !String.class.equals(type)) {
                 throw new IllegalStateException("Context is required for none-string value flags");
             }