Streamify SWCommand

SpigotCore_Main/src/de/steamwar/command/SWCommand.java

@@ -60,12 +60,10 @@ public abstract class SWCommand {
 
             @Override
             public List<String> tabComplete(CommandSender sender, String alias, String[] args) throws IllegalArgumentException {
-                List<String> strings = new ArrayList<>();
-                for (SubCommand subCommand : commandList) {
-                    List<String> tabCompletes = subCommand.tabComplete(sender, args);
-                    if (tabCompletes != null) strings.addAll(tabCompletes);
-                }
-                return strings.stream()
+                return commandList.stream()
+                        .map(s -> s.tabComplete(sender, args))
+                        .filter(Objects::nonNull)
+                        .flatMap(Collection::stream)
                         .filter(s -> !s.isEmpty())
                         .filter(s -> !s.isBlank())
                         .filter(s -> s.toLowerCase().startsWith(args[args.length - 1].toLowerCase()))