Allow omitting Subject and From for hosted-template sends (#117)

src/Resend/EmailMessage.cs

@@ -10,8 +10,13 @@ public class EmailMessage
     /// <summary>
     /// Sender email address.
     /// </summary>
+    /// <remarks>
+    /// Can be omitted when sending a hosted <see cref="Template" /> that
+    /// defines a default sender.
+    /// </remarks>
     [JsonPropertyName( "from" )]
-    public EmailAddress From { get; set; } = default!;
+    [JsonIgnore( Condition = JsonIgnoreCondition.WhenWritingNull )]
+    public EmailAddress? From { get; set; }
 
     /// <summary>
     /// Recipient email address (list).
@@ -22,8 +27,13 @@ public class EmailMessage
     /// <summary>
     /// Email subject.
     /// </summary>
+    /// <remarks>
+    /// Can be omitted when sending a hosted <see cref="Template" /> that
+    /// defines a default subject.
+    /// </remarks>
     [JsonPropertyName( "subject" )]
-    public string Subject { get; set; } = default!;
+    [JsonIgnore( Condition = JsonIgnoreCondition.WhenWritingNull )]
+    public string? Subject { get; set; }
 
     /// <summary>
     /// Cc/carbon-copy recipient email address.

tests/Resend.Tests/EmailMessageTests.cs

@@ -0,0 +1,40 @@
+using System.Text.Json;
+
+namespace Resend.Tests;
+
+/// <summary />
+public class EmailMessageTests
+{
+    /// <summary />
+    [Fact]
+    public void OmitsSubjectAndFromWhenNull()
+    {
+        var message = new EmailMessage()
+        {
+            To = "to@example.com",
+        };
+
+        var json = JsonSerializer.Serialize( message );
+
+        Assert.DoesNotContain( "\"subject\"", json );
+        Assert.DoesNotContain( "\"from\"", json );
+    }
+
+
+    /// <summary />
+    [Fact]
+    public void IncludesSubjectAndFromWhenSet()
+    {
+        var message = new EmailMessage()
+        {
+            From = "from@example.com",
+            To = "to@example.com",
+            Subject = "Hello",
+        };
+
+        var json = JsonSerializer.Serialize( message );
+
+        Assert.Contains( "\"subject\":\"Hello\"", json );
+        Assert.Contains( "\"from\"", json );
+    }
+}