fix: Guarding against empty descriptions in SlashCommandBuilder/SlashCommandOptionBuilder (#2260)

* adding null/empty check for option-descriptions

* moving check to Preconditions

* docs

src/Discord.Net.Core/Utils/Preconditions.cs

@@ -297,5 +297,22 @@ namespace Discord
             }
         }
         #endregion
+
+        #region SlashCommandOptions
+
+        /// <exception cref="ArgumentNullException"><paramref name="description"/> or <paramref name="name"/> is null.</exception>
+        /// <exception cref="ArgumentException"><paramref name="description"/> or <paramref name="name"/> are either empty or their length exceed limits.</exception>
+        public static void Options(string name, string description)
+        {
+            // Make sure the name matches the requirements from discord
+            NotNullOrEmpty(name, nameof(name));
+            NotNullOrEmpty(description, nameof(description));
+            AtLeast(name.Length, 1, nameof(name));
+            AtMost(name.Length, SlashCommandBuilder.MaxNameLength, nameof(name));
+            AtLeast(description.Length, 1, nameof(description));
+            AtMost(description.Length, SlashCommandBuilder.MaxDescriptionLength, nameof(description));
+        }
+
+        #endregion
     }
 }