Fix BasicCommand suggestion arg count

Resolves: #11211
Backport-of: #11241

patches/server/1042-Brigadier-based-command-API.patch

@@ -686,10 +686,10 @@ index 0000000000000000000000000000000000000000..1b1642f306771f029e6214a2e2ebebb6
 +}
 diff --git a/src/main/java/io/papermc/paper/command/brigadier/PaperCommands.java b/src/main/java/io/papermc/paper/command/brigadier/PaperCommands.java
 new file mode 100644
-index 0000000000000000000000000000000000000000..27509813a90980be1dfc7bde27d0eba60adfc820
+index 0000000000000000000000000000000000000000..c0d2268c6f79bad107a490f8fa1c746a6a96b573
 --- /dev/null
 +++ b/src/main/java/io/papermc/paper/command/brigadier/PaperCommands.java
-@@ -0,0 +1,193 @@
+@@ -0,0 +1,199 @@
 +package io.papermc.paper.command.brigadier;
 +
 +import com.google.common.base.Preconditions;
@@ -710,6 +710,7 @@ index 0000000000000000000000000000000000000000..27509813a90980be1dfc7bde27d0eba6
 +import java.util.Locale;
 +import java.util.Set;
 +import net.minecraft.commands.CommandBuildContext;
++import org.apache.commons.lang3.ArrayUtils;
 +import org.apache.commons.lang3.StringUtils;
 +import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
 +import org.checkerframework.checker.nullness.qual.NonNull;
@@ -863,7 +864,12 @@ index 0000000000000000000000000000000000000000..27509813a90980be1dfc7bde27d0eba6
 +            .then(
 +                Commands.argument("args", StringArgumentType.greedyString())
 +                    .suggests((context, suggestionsBuilder) -> {
-+                        final String[] args = StringUtils.split(suggestionsBuilder.getRemaining());
++                        String[] args = StringUtils.split(suggestionsBuilder.getRemaining());
++                        if (suggestionsBuilder.getRemaining().endsWith(" ")) {
++                            // if there is trailing whitespace, we should add an empty argument to signify
++                            // that there may be more, but no characters have been typed yet
++                            args = ArrayUtils.add(args, "");
++                        }
 +                        final SuggestionsBuilder offsetSuggestionsBuilder = suggestionsBuilder.createOffset(suggestionsBuilder.getInput().lastIndexOf(' ') + 1);;
 +
 +                        final Collection<String> suggestions = basicCommand.suggest(context.getSource(), args);