diff --git a/OpenTween/Api/DataModel/TwitterUser.cs b/OpenTween/Api/DataModel/TwitterUser.cs
index f5dfc1e07..971f05045 100644
--- a/OpenTween/Api/DataModel/TwitterUser.cs
+++ b/OpenTween/Api/DataModel/TwitterUser.cs
@@ -85,8 +85,10 @@ public class TwitterUserEntity
         [DataMember(Name = "profile_banner_url")]
         public string ProfileBannerUrl { get; set; }
 
+        // ProfileImageUrlHttps が null になる場合があるらしい
+        // 参照: https://sourceforge.jp/ticket/browse.php?group_id=6526&tid=33871
         [DataMember(Name = "profile_image_url_https")]
-        public string ProfileImageUrlHttps { get; set; }
+        public string? ProfileImageUrlHttps { get; set; }
 
         [DataMember(Name = "protected")]
         public bool Protected { get; set; }
@@ -120,7 +122,7 @@ public static TwitterUser CreateUnknownUser()
                 IdStr = "0",
                 ScreenName = "?????",
                 Name = "Unknown User",
-                ProfileImageUrlHttps = "",
+                ProfileImageUrlHttps = null,
             };
         }
     }
diff --git a/OpenTween/Api/GraphQL/TwitterGraphqlUser.cs b/OpenTween/Api/GraphQL/TwitterGraphqlUser.cs
index cc6a506aa..4d3af4eb5 100644
--- a/OpenTween/Api/GraphQL/TwitterGraphqlUser.cs
+++ b/OpenTween/Api/GraphQL/TwitterGraphqlUser.cs
@@ -75,7 +75,7 @@ static string GetText(XElement elm, string name)
             {
                 IdStr = GetText(userElm, "rest_id"),
                 Name = GetText(userLegacyElm, "name"),
-                ProfileImageUrlHttps = GetText(userLegacyElm, "profile_image_url_https"),
+                ProfileImageUrlHttps = GetTextOrNull(userLegacyElm, "profile_image_url_https"),
                 ScreenName = GetText(userLegacyElm, "screen_name"),
                 Protected = GetTextOrNull(userLegacyElm, "protected") == "true",
                 Verified = GetTextOrNull(userLegacyElm, "verified") == "true",
diff --git a/OpenTween/Models/PostClass.cs b/OpenTween/Models/PostClass.cs
index 873e53b37..33357e731 100644
--- a/OpenTween/Models/PostClass.cs
+++ b/OpenTween/Models/PostClass.cs
@@ -53,7 +53,7 @@ double Latitude
         /// <summary>スクリーンリーダーでの読み上げを考慮したテキスト</summary>
         public string AccessibleText { get; init; } = "";
 
-        public string ImageUrl { get; init; } = "";
+        public string? ImageUrl { get; init; }
 
         public string ScreenName { get; init; } = "";
 
diff --git a/OpenTween/SocialProtocol/Twitter/TwitterPostFactory.cs b/OpenTween/SocialProtocol/Twitter/TwitterPostFactory.cs
index c6419e41c..c23c876de 100644
--- a/OpenTween/SocialProtocol/Twitter/TwitterPostFactory.cs
+++ b/OpenTween/SocialProtocol/Twitter/TwitterPostFactory.cs
@@ -137,7 +137,9 @@ public PostClass CreateFromStatus(
             // 他の発言と重複しやすい (共通化できる) 文字列は string.Intern を通す
             var screenName = string.Intern(originalStatusUser.ScreenName);
             var nickname = string.Intern(originalStatusUser.Name);
-            var imageUrl = string.Intern(originalStatusUser.ProfileImageUrlHttps);
+            var imageUrl = originalStatusUser.ProfileImageUrlHttps is { } profileImageUrl
+                ? string.Intern(profileImageUrl)
+                : null;
 
             // Source整形
             var (sourceText, sourceUri) = ParseSource(originalStatus.Source);
@@ -265,7 +267,9 @@ bool firstLoad
             // 他の発言と重複しやすい (共通化できる) 文字列は string.Intern を通す
             var screenName = string.Intern(displayUser.ScreenName);
             var nickname = string.Intern(displayUser.Name);
-            var imageUrl = string.Intern(displayUser.ProfileImageUrlHttps);
+            var imageUrl = displayUser.ProfileImageUrlHttps is { } imageUrlStr
+                ? string.Intern(imageUrlStr)
+                : null;
 
             var source = (string?)null;
             var sourceUri = (Uri?)null;
diff --git a/OpenTween/Tween.cs b/OpenTween/Tween.cs
index 1785a744d..7a2b5b607 100644
--- a/OpenTween/Tween.cs
+++ b/OpenTween/Tween.cs
@@ -972,8 +972,11 @@ private void NotifyNewPosts(PostClass[] notifyPosts, string soundFile, int addCo
                             var bText = sb.ToString();
                             if (MyCommon.IsNullOrEmpty(bText)) return;
 
-                            var image = this.iconCache.TryGetFromCache(post.ImageUrl);
-                            this.gh.Notify(nt, post.StatusId.Id, title.ToString(), bText, image?.Image, post.ImageUrl);
+                            var image = post.ImageUrl is { } imageUrl
+                                ? this.iconCache.TryGetFromCache(imageUrl)
+                                : null;
+
+                            this.gh.Notify(nt, post.StatusId.Id, title.ToString(), bText, image?.Image);
                         }
                     }
                     else
diff --git a/OpenTween/TweetDetailsView.cs b/OpenTween/TweetDetailsView.cs
index 9cfa79129..cfb7a4f1e 100644
--- a/OpenTween/TweetDetailsView.cs
+++ b/OpenTween/TweetDetailsView.cs
@@ -268,7 +268,7 @@ public HtmlElement[] GetLinkElements()
                 .ToArray();
         }
 
-        private async Task SetUserPictureAsync(string normalImageUrl, bool force = false)
+        private async Task SetUserPictureAsync(string? normalImageUrl, bool force = false)
         {
             if (MyCommon.IsNullOrEmpty(normalImageUrl))
                 return;
@@ -627,7 +627,7 @@ private void ContextMenuUserPicture_Opening(object sender, CancelEventArgs e)
 
                     this.ReloadIconToolStripMenuItem.Enabled = true;
 
-                    if (this.IconCache.TryGetFromCache(this.CurrentPost.ImageUrl) != null)
+                    if (this.CurrentPost.ImageUrl is { } imageUrl && this.IconCache.TryGetFromCache(imageUrl) != null)
                     {
                         this.SaveIconPictureToolStripMenuItem.Enabled = true;
                     }
diff --git a/OpenTween/UserInfo.cs b/OpenTween/UserInfo.cs
index a725fbdd1..c23d0f265 100644
--- a/OpenTween/UserInfo.cs
+++ b/OpenTween/UserInfo.cs
@@ -47,14 +47,9 @@ public UserInfo(TwitterUser user)
             this.ScreenName = user.ScreenName;
             this.Location = WebUtility.HtmlDecode(user.Location);
             this.Description = WebUtility.HtmlDecode(user.Description);
-            try
-            {
-                this.ImageUrl = new Uri(user.ProfileImageUrlHttps);
-            }
-            catch (Exception)
-            {
-                this.ImageUrl = null;
-            }
+            this.ImageUrl = user.ProfileImageUrlHttps is { } imageUrlStr
+                ? new Uri(imageUrlStr)
+                : null;
             this.Url = user.Url ?? "";
             this.Protect = user.Protected;
             this.FriendsCount = user.FriendsCount;
diff --git a/OpenTween/UserInfoDialog.cs b/OpenTween/UserInfoDialog.cs
index 9b99236e6..f720bb422 100644
--- a/OpenTween/UserInfoDialog.cs
+++ b/OpenTween/UserInfoDialog.cs
@@ -194,14 +194,12 @@ private async Task SetDescriptionAsync(string? descriptionText, TwitterEntities?
             }
         }
 
-        private async Task SetUserImageAsync(string imageUri, CancellationToken cancellationToken)
+        private async Task SetUserImageAsync(string? imageUri, CancellationToken cancellationToken)
         {
             var oldImage = this.UserPicture.Image;
             this.UserPicture.Image = null;
             oldImage?.Dispose();
 
-            // ProfileImageUrlHttps が null になる場合があるらしい
-            // 参照: https://sourceforge.jp/ticket/browse.php?group_id=6526&tid=33871
             if (imageUri == null)
                 return;
 
@@ -468,6 +466,9 @@ private async void ButtonSearchPosts_Click(object sender, EventArgs e)
         private async void UserPicture_Click(object sender, EventArgs e)
         {
             var imageUrl = this.displayUser.ProfileImageUrlHttps;
+            if (imageUrl == null)
+                return;
+
             imageUrl = TwitterLegacy.CreateProfileImageUrl(imageUrl, "original");
 
             await MyCommon.OpenInBrowserAsync(this, imageUrl);