Add command-related utility functions

src/dev/w1zzrd/invtweaks/command/CommandUtils.java

@@ -0,0 +1,19 @@
+package dev.w1zzrd.invtweaks.command;
+
+import net.md_5.bungee.api.ChatColor;
+import net.md_5.bungee.api.chat.TextComponent;
+import org.bukkit.command.CommandSender;
+
+public final class CommandUtils {
+    private CommandUtils() { throw new UnsupportedOperationException("Functional class"); }
+
+    public static boolean assertTrue(final boolean condition, final String message, final CommandSender sender) {
+        if (!condition) {
+            final TextComponent errorMessage = new TextComponent(message);
+            errorMessage.setColor(ChatColor.DARK_RED);
+            sender.spigot().sendMessage(errorMessage);
+        }
+
+        return !condition;
+    }
+}