Only allow messages with an embed present to be sent with no content

src/Discord.Net.Core/API/DiscordRestApiClient.cs

@@ -439,7 +439,10 @@ namespace Discord.API
         {
             Preconditions.NotEqual(channelId, 0, nameof(channelId));
             Preconditions.NotNull(args, nameof(args));
-            if (args.Content.GetValueOrDefault()?.Length > DiscordConfig.MaxMessageSize)
+            if (!args.Embed.IsSpecified || args.Embed.Value == null)
+                Preconditions.NotNullOrEmpty(args.Content, nameof(args.Content));
+
+            if (args.Content.Length > DiscordConfig.MaxMessageSize)
                 throw new ArgumentException($"Message content is too long, length must be less or equal to {DiscordConfig.MaxMessageSize}.", nameof(args.Content));
             options = RequestOptions.CreateOrClone(options);
 

src/Discord.Net.Core/API/Rest/CreateMessageParams.cs

@@ -8,7 +8,8 @@ namespace Discord.API.Rest
     public class CreateMessageParams
     {
         [JsonProperty("content")]
-        public Optional<string> Content { get; }
+        public string Content { get; }
+
         [JsonProperty("nonce")]
         public Optional<string> Nonce { get; set; }
         [JsonProperty("tts")]
@@ -18,10 +19,7 @@ namespace Discord.API.Rest
 
         public CreateMessageParams(string content)
         {
-            if (string.IsNullOrEmpty(content))
-                Content = Optional.Create<string>();
-            else
-                Content = content;
+            Content = content;
         }
     }
 }