Adding checks for the other URL properties

src/Discord.Net.Rest/Entities/Messages/EmbedBuilder.cs

@@ -44,7 +44,7 @@ namespace Discord
             get => _embed.Url;
             set
             {
-                if (!Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(Url));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(Url));
                 _embed.Url = value;
             }
         }
@@ -53,7 +53,7 @@ namespace Discord
             get => _embed.Thumbnail?.Url;
             set
             {
-                if (!Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(ThumbnailUrl));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(ThumbnailUrl));
                 _embed.Thumbnail = new EmbedThumbnail(value, null, null, null);
             }
         }
@@ -62,7 +62,7 @@ namespace Discord
             get => _embed.Image?.Url;
             set
             {
-                if (!Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(ImageUrl));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(ImageUrl));
                 _embed.Image = new EmbedImage(value, null, null, null);
             }
         }
@@ -313,7 +313,7 @@ namespace Discord
             get => _author.Url;
             set
             {
-                if (!Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(Url));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(Url));
                 _author.Url = value;
             }
         }
@@ -322,7 +322,7 @@ namespace Discord
             get => _author.IconUrl;
             set
             {
-                if (!Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(IconUrl));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(IconUrl));
                 _author.IconUrl = value;
             }
         }
@@ -372,7 +372,7 @@ namespace Discord
             get => _footer.IconUrl;
             set
             {
-                if (value != null && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(IconUrl));
+                if (!string.IsNullOrEmpty(value) && !Uri.IsWellFormedUriString(value, UriKind.Absolute)) throw new ArgumentException("Url must be a well-formed URI", nameof(IconUrl));
                 _footer.IconUrl = value;
             }
         }