diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbCipTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbCipTagConfigEditor.razor
index a845ebba..5a039f7e 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbCipTagConfigEditor.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbCipTagConfigEditor.razor
@@ -28,8 +28,6 @@
         _m = AbCipTagConfigModel.FromJson(ConfigJson);
     }
 
-    private static int ParseInt(object? v, int fallback = 0) => int.TryParse(v?.ToString(), out var i) ? i : fallback;
-
     // TryParse so a bad/empty change value can never throw into the Blazor circuit — it falls back.
     private static TEnum ParseEnum<TEnum>(object? v, TEnum fallback) where TEnum : struct, Enum
         => Enum.TryParse<TEnum>(v?.ToString(), out var r) ? r : fallback;
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbLegacyTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbLegacyTagConfigEditor.razor
index 66526cf0..77014b05 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbLegacyTagConfigEditor.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/AbLegacyTagConfigEditor.razor
@@ -28,8 +28,6 @@
         _m = AbLegacyTagConfigModel.FromJson(ConfigJson);
     }
 
-    private static int ParseInt(object? v, int fallback = 0) => int.TryParse(v?.ToString(), out var i) ? i : fallback;
-
     // TryParse so a bad/empty change value can never throw into the Blazor circuit — it falls back.
     private static TEnum ParseEnum<TEnum>(object? v, TEnum fallback) where TEnum : struct, Enum
         => Enum.TryParse<TEnum>(v?.ToString(), out var r) ? r : fallback;
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
index cff7e878..8c7bd56e 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
@@ -28,8 +28,6 @@
         _m = FocasTagConfigModel.FromJson(ConfigJson);
     }
 
-    private static int ParseInt(object? v, int fallback = 0) => int.TryParse(v?.ToString(), out var i) ? i : fallback;
-
     // TryParse so a bad/empty change value can never throw into the Blazor circuit — it falls back.
     private static TEnum ParseEnum<TEnum>(object? v, TEnum fallback) where TEnum : struct, Enum
         => Enum.TryParse<TEnum>(v?.ToString(), out var r) ? r : fallback;
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/TwinCATTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/TwinCATTagConfigEditor.razor
index b8371ab6..af11e1d2 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/TwinCATTagConfigEditor.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/TwinCATTagConfigEditor.razor
@@ -28,8 +28,6 @@
         _m = TwinCATTagConfigModel.FromJson(ConfigJson);
     }
 
-    private static int ParseInt(object? v, int fallback = 0) => int.TryParse(v?.ToString(), out var i) ? i : fallback;
-
     // TryParse so a bad/empty change value can never throw into the Blazor circuit — it falls back.
     private static TEnum ParseEnum<TEnum>(object? v, TEnum fallback) where TEnum : struct, Enum
         => Enum.TryParse<TEnum>(v?.ToString(), out var r) ? r : fallback;
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
index 33e15e73..673dd433 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/TagConfigJson.cs
@@ -33,7 +33,10 @@ public static class TagConfigJson
     public static TEnum GetEnum<TEnum>(JsonObject o, string name, TEnum fallback) where TEnum : struct, Enum
         => GetString(o, name) is { } s && Enum.TryParse<TEnum>(s, ignoreCase: true, out var v) ? v : fallback;
 
-    /// <summary>Sets a string/number/enum-name value (enums via ToString()). Null removes the key.</summary>
+    /// <summary>Sets a string/number/enum-name value (enums via ToString()). A null value REMOVES the key, so it is omitted from the serialised JSON.</summary>
     public static void Set(JsonObject o, string name, object? value)
-        => o[name] = value is null ? null : JsonValue.Create(value is Enum e ? e.ToString() : value);
+    {
+        if (value is null) { o.Remove(name); return; }
+        o[name] = JsonValue.Create(value is Enum e ? e.ToString() : value);
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbCipTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbCipTagConfigModelTests.cs
index ea5a8405..73fb1c41 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbCipTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbCipTagConfigModelTests.cs
@@ -79,4 +79,24 @@ public sealed class AbCipTagConfigModelTests
     {
         new AbCipTagConfigModel { TagPath = "Motor1.Status" }.Validate().ShouldBeNull();
     }
+
+    [Fact]
+    public void ToJson_omits_blank_deviceHostAddress()
+    {
+        var m = new AbCipTagConfigModel { TagPath = "Motor1.Status", DeviceHostAddress = "" };
+
+        var json = m.ToJson();
+
+        json.ShouldNotContain("deviceHostAddress");
+    }
+
+    [Fact]
+    public void ToJson_includes_deviceHostAddress_when_set()
+    {
+        var m = new AbCipTagConfigModel { TagPath = "Motor1.Status", DeviceHostAddress = "ab://host" };
+
+        var json = m.ToJson();
+
+        json.ShouldContain("\"deviceHostAddress\":\"ab://host\"");
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbLegacyTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbLegacyTagConfigModelTests.cs
index f900a834..6552bcb5 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbLegacyTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/AbLegacyTagConfigModelTests.cs
@@ -79,4 +79,24 @@ public sealed class AbLegacyTagConfigModelTests
     {
         new AbLegacyTagConfigModel { Address = "N7:0" }.Validate().ShouldBeNull();
     }
+
+    [Fact]
+    public void ToJson_omits_blank_deviceHostAddress()
+    {
+        var m = new AbLegacyTagConfigModel { Address = "N7:0", DeviceHostAddress = "" };
+
+        var json = m.ToJson();
+
+        json.ShouldNotContain("deviceHostAddress");
+    }
+
+    [Fact]
+    public void ToJson_includes_deviceHostAddress_when_set()
+    {
+        var m = new AbLegacyTagConfigModel { Address = "N7:0", DeviceHostAddress = "ab://host" };
+
+        var json = m.ToJson();
+
+        json.ShouldContain("\"deviceHostAddress\":\"ab://host\"");
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
index 03a1ff28..f7dbca89 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
@@ -79,4 +79,24 @@ public sealed class FocasTagConfigModelTests
     {
         new FocasTagConfigModel { Address = "R100" }.Validate().ShouldBeNull();
     }
+
+    [Fact]
+    public void ToJson_omits_blank_deviceHostAddress()
+    {
+        var m = new FocasTagConfigModel { Address = "R100", DeviceHostAddress = "" };
+
+        var json = m.ToJson();
+
+        json.ShouldNotContain("deviceHostAddress");
+    }
+
+    [Fact]
+    public void ToJson_includes_deviceHostAddress_when_set()
+    {
+        var m = new FocasTagConfigModel { Address = "R100", DeviceHostAddress = "ab://host" };
+
+        var json = m.ToJson();
+
+        json.ShouldContain("\"deviceHostAddress\":\"ab://host\"");
+    }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TagConfigJsonTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TagConfigJsonTests.cs
index 87e2f0d9..e1d4e454 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TagConfigJsonTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TagConfigJsonTests.cs
@@ -129,6 +129,7 @@ public sealed class TagConfigJsonTests
 
         TagConfigJson.Set(obj, "region", null);
 
-        TagConfigJson.GetString(obj, "region").ShouldBeNull();
+        obj.ContainsKey("region").ShouldBeFalse();
+        TagConfigJson.Serialize(obj).ShouldNotContain("region");
     }
 }
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TwinCATTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TwinCATTagConfigModelTests.cs
index 435edc89..1871c850 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TwinCATTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TwinCATTagConfigModelTests.cs
@@ -79,4 +79,24 @@ public sealed class TwinCATTagConfigModelTests
     {
         new TwinCATTagConfigModel { SymbolPath = "MAIN.bStart" }.Validate().ShouldBeNull();
     }
+
+    [Fact]
+    public void ToJson_omits_blank_deviceHostAddress()
+    {
+        var m = new TwinCATTagConfigModel { SymbolPath = "MAIN.bStart", DeviceHostAddress = "" };
+
+        var json = m.ToJson();
+
+        json.ShouldNotContain("deviceHostAddress");
+    }
+
+    [Fact]
+    public void ToJson_includes_deviceHostAddress_when_set()
+    {
+        var m = new TwinCATTagConfigModel { SymbolPath = "MAIN.bStart", DeviceHostAddress = "ab://host" };
+
+        var json = m.ToJson();
+
+        json.ShouldContain("\"deviceHostAddress\":\"ab://host\"");
+    }
 }