fix: omit null table from postgres_changes join payload

Realtime/PostgresChanges/PostgresChangesOptions.cs

@@ -57,9 +57,11 @@ public enum ListenType
     public string Schema { get; set; }
 
     /// <summary>
-    /// The table for this listener, can be: `*` matching all tables in schema.
+    /// The table for this listener, can be: `*` matching all tables in schema. When <c>null</c>
+    /// (a schema-wide listener), the <c>table</c> key is omitted from the join payload rather than
+    /// sent as <c>null</c>.
     /// </summary>
-    [JsonProperty("table")]
+    [JsonProperty("table", NullValueHandling = NullValueHandling.Ignore)]
     public string? Table { get; set; }
 
     /// <summary>

RealtimeTests/Serialization/PostgresChangesOptionsTests.cs

@@ -0,0 +1,29 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using Supabase.Realtime.PostgresChanges;
+
+namespace RealtimeTests;
+
+/// <summary>
+/// Wire-shape of <see cref="PostgresChangesOptions"/> as it is serialized into a channel's
+/// join <c>config.postgres_changes</c> payload.
+/// </summary>
+[TestClass]
+public class PostgresChangesOptionsTests
+{
+    [TestMethod]
+    public void Table_ShouldBeOmittedFromJson_WhenNull()
+    {
+        // A schema-wide listener has no table; the server expects the key absent, not `"table": null`.
+        var json = JsonConvert.SerializeObject(new PostgresChangesOptions("public"));
+        Assert.IsFalse(JObject.Parse(json).ContainsKey("table"));
+    }
+
+    [TestMethod]
+    public void Table_ShouldBeSerialized_WhenProvided()
+    {
+        var json = JsonConvert.SerializeObject(new PostgresChangesOptions("public", "todos"));
+        Assert.AreEqual("todos", JObject.Parse(json)["table"]?.Value<string>());
+    }
+}