diff --git a/src/MagicOnion.Abstractions/UnaryResult.cs b/src/MagicOnion.Abstractions/UnaryResult.cs
index 49dd68792..58b1b574c 100644
--- a/src/MagicOnion.Abstractions/UnaryResult.cs
+++ b/src/MagicOnion.Abstractions/UnaryResult.cs
@@ -58,7 +58,7 @@ public UnaryResult(Task<TResponse> rawTaskValue)
         {
             this.hasRawValue = true;
             this.rawValue = default(TResponse);
-            this.rawTaskValue = rawTaskValue;
+            this.rawTaskValue = rawTaskValue ?? throw new ArgumentNullException(nameof(rawTaskValue));
             this.response = null;
         }
 
@@ -67,7 +67,7 @@ public UnaryResult(Task<IResponseContext<TResponse>> response)
             this.hasRawValue = false;
             this.rawValue = default(TResponse);
             this.rawTaskValue = null;
-            this.response = response;
+            this.response = response ?? throw new ArgumentNullException(nameof(response));
         }
 
         /// <summary>
@@ -79,6 +79,13 @@ public Task<TResponse> ResponseAsync
             {
                 if (!hasRawValue)
                 {
+                    // If the UnaryResult has no raw-value and no response, it is the default value of UnaryResult<TResponse>.
+                    // So, we will return the default value of TResponse as Task.
+                    if (response is null)
+                    {
+                        return Task.FromResult(default(TResponse));
+                    }
+
                     return UnwrapResponse();
                 }
                 else if (rawTaskValue != null)
diff --git a/src/MagicOnion.Client.Unity/Assets/Scripts/MagicOnion/MagicOnion.Abstractions/UnaryResult.cs b/src/MagicOnion.Client.Unity/Assets/Scripts/MagicOnion/MagicOnion.Abstractions/UnaryResult.cs
index 49dd68792..58b1b574c 100644
--- a/src/MagicOnion.Client.Unity/Assets/Scripts/MagicOnion/MagicOnion.Abstractions/UnaryResult.cs
+++ b/src/MagicOnion.Client.Unity/Assets/Scripts/MagicOnion/MagicOnion.Abstractions/UnaryResult.cs
@@ -58,7 +58,7 @@ public UnaryResult(Task<TResponse> rawTaskValue)
         {
             this.hasRawValue = true;
             this.rawValue = default(TResponse);
-            this.rawTaskValue = rawTaskValue;
+            this.rawTaskValue = rawTaskValue ?? throw new ArgumentNullException(nameof(rawTaskValue));
             this.response = null;
         }
 
@@ -67,7 +67,7 @@ public UnaryResult(Task<IResponseContext<TResponse>> response)
             this.hasRawValue = false;
             this.rawValue = default(TResponse);
             this.rawTaskValue = null;
-            this.response = response;
+            this.response = response ?? throw new ArgumentNullException(nameof(response));
         }
 
         /// <summary>
@@ -79,6 +79,13 @@ public Task<TResponse> ResponseAsync
             {
                 if (!hasRawValue)
                 {
+                    // If the UnaryResult has no raw-value and no response, it is the default value of UnaryResult<TResponse>.
+                    // So, we will return the default value of TResponse as Task.
+                    if (response is null)
+                    {
+                        return Task.FromResult(default(TResponse));
+                    }
+
                     return UnwrapResponse();
                 }
                 else if (rawTaskValue != null)
diff --git a/tests/MagicOnion.Server.Tests/UnaryResultTest.cs b/tests/MagicOnion.Server.Tests/UnaryResultTest.cs
new file mode 100644
index 000000000..a8d8ede09
--- /dev/null
+++ b/tests/MagicOnion.Server.Tests/UnaryResultTest.cs
@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using System.Threading.Tasks;
+using FluentAssertions;
+using Grpc.Core;
+using MagicOnion.Client;
+using Xunit;
+
+namespace MagicOnion.Server.Tests
+{
+    public class UnaryResultTest
+    {
+        [Fact]
+        public async Task FromResult()
+        {
+            (await UnaryResult.FromResult(123)).Should().Be(123);
+            (await UnaryResult.FromResult("foo")).Should().Be("foo");
+            (await UnaryResult.FromResult<string>(default(string))).Should().BeNull();
+
+            Assert.Throws<ArgumentNullException>(() => UnaryResult.FromResult(default(Task<string>)));
+        }
+
+        [Fact]
+        public async Task Ctor_RawValue()
+        {
+            var result = new UnaryResult<int>(123);
+            (await result).Should().Be(123);
+
+            var result2 = new UnaryResult<string>("foo");
+            (await result2).Should().Be("foo");
+
+            var result3 = new UnaryResult<string>(default(string));
+            (await result3).Should().BeNull();
+        }
+
+        [Fact]
+        public async Task Ctor_RawTask()
+        {
+            var result = new UnaryResult<int>(Task.FromResult(456));
+            (await result).Should().Be(456);
+
+            var result2 = new UnaryResult<string>(Task.FromResult("foo"));
+            (await result2).Should().Be("foo");
+
+            Assert.Throws<ArgumentNullException>(() => new UnaryResult<string>(default(Task<string>)));
+        }
+
+        [Fact]
+        public async Task Ctor_TaskOfResponseContext()
+        {
+            var result = new UnaryResult<int>(Task.FromResult(DummyResponseContext.Create(456)));
+            (await result).Should().Be(456);
+
+            var result2 = new UnaryResult<string>(Task.FromResult(DummyResponseContext.Create("foo")));
+            (await result2).Should().Be("foo");
+
+            Assert.Throws<ArgumentNullException>(() => new UnaryResult<string>(default(Task<IResponseContext<string>>)));
+        }
+
+        static class DummyResponseContext
+        {
+            public static IResponseContext<T> Create<T>(T value)
+                => new DummyResponseContext<T>(value);
+        }
+        class DummyResponseContext<T> : IResponseContext<T>
+        {
+            readonly T value;
+
+            public DummyResponseContext(T value)
+            {
+                this.value = value;
+            }
+
+            public Task<Metadata> ResponseHeadersAsync => Task.FromResult(Metadata.Empty);
+            public Status GetStatus() => Status.DefaultSuccess;
+            public Metadata GetTrailers() => Metadata.Empty;
+
+            public Type ResponseType => typeof(T);
+            public Task<T> ResponseAsync => Task.FromResult(value);
+
+            public void Dispose() { }
+
+        }
+
+        [Fact]
+        public async Task Ctor_Default()
+        {
+            var result = default(UnaryResult<int>);
+            (await result).Should().Be(0);
+
+            var result2 = default(UnaryResult<string>);
+            (await result2).Should().Be(null);
+        }
+    }
+}