diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingDictionariesInCSharp.Benchmark.csproj b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingDictionariesInCSharp.Benchmark.csproj
index 218beee44b..dc6f04d43e 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingDictionariesInCSharp.Benchmark.csproj
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingDictionariesInCSharp.Benchmark.csproj
@@ -2,13 +2,13 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="BenchmarkDotNet" Version="0.13.5" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.15.8" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingMethodsBenchmark.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingMethodsBenchmark.cs
index a8fe46264d..b4136b13d7 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingMethodsBenchmark.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/MergingMethodsBenchmark.cs
@@ -8,27 +8,24 @@
 [RankColumn]
 public class MergingMethodsBenchmark
 {
-    private Dictionary<int, string> _dictionaryA;
-    private Dictionary<int, string> _dictionaryB;
+    private readonly Dictionary<int, string> _dictionaryA = [];
+    private readonly Dictionary<int, string> _dictionaryB = [];
 
     [GlobalSetup]
     public void Setup()
     {
-        _dictionaryA = new Dictionary<int, string>();
-        _dictionaryB = new Dictionary<int, string>();
-
         // Generate random values for dictionaryA
         for (var i = 0; i < 100; i++)
         {
             var randomValue = GenerateRandomValue();
-            _dictionaryA.Add(i, randomValue);            
+            _dictionaryA.Add(i, randomValue);
         }
 
         // Generate random values for dictionaryB
-        for (int i = 100; i < 200; i++)
+        for (var i = 100; i < 200; i++)
         {
             var randomValue = GenerateRandomValue();
-            _dictionaryB.Add(i, randomValue);            
+            _dictionaryB.Add(i, randomValue);
         }
     }
 
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/Program.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/Program.cs
index 9dca772280..9dbefa1337 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/Program.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Benchmark/Program.cs
@@ -1 +1 @@
-BenchmarkDotNet.Running.BenchmarkRunner.Run<MergingMethodsBenchmark>();
\ No newline at end of file
+BenchmarkDotNet.Running.BenchmarkRunner.Run<MergingMethodsBenchmark>(args: args);
\ No newline at end of file
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/MergingDictionariesInCSharp.Tests.csproj b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/MergingDictionariesInCSharp.Tests.csproj
index 89e365a787..09759a3601 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/MergingDictionariesInCSharp.Tests.csproj
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/MergingDictionariesInCSharp.Tests.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
@@ -9,11 +9,11 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.3.2" />
-    <PackageReference Include="NUnit" Version="3.13.3" />
-    <PackageReference Include="NUnit3TestAdapter" Version="4.2.1" />
-    <PackageReference Include="NUnit.Analyzers" Version="3.3.0" />
-    <PackageReference Include="coverlet.collector" Version="3.1.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
+    <PackageReference Include="NUnit" Version="5.0.0" />
+    <PackageReference Include="NUnit3TestAdapter" Version="6.3.1" />
+    <PackageReference Include="NUnit.Analyzers" Version="4.15.0" />
+    <PackageReference Include="coverlet.collector" Version="10.1.0" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/UnitTests.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/UnitTests.cs
index e31e43d755..cf03a12c72 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/UnitTests.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.Tests/UnitTests.cs
@@ -3,9 +3,10 @@
 [TestFixture]
 public class MergingMethodsTests
 {
-    private Dictionary<int, string> _dictionaryA;
-    private Dictionary<int, string> _dictionaryB;
-    private Dictionary<int, string> _expectedMergedDictionary;
+    private Dictionary<int, string> _dictionaryA = [];
+    private Dictionary<int, string> _dictionaryB = [];
+    private Dictionary<int, string> _expectedMergedDictionary = [];
+    private Dictionary<int, string> _clashingDictionary = [];
 
     [SetUp]
     public void SetUp()
@@ -33,6 +34,12 @@ public void SetUp()
             { 5, "Watermelon" },
             { 6, "Pineapple" }
         };
+
+        // key 1 already exists in _dictionaryA, with a different value
+        _clashingDictionary = new Dictionary<int, string>()
+        {
+            { 1, "Watermelon" }
+        };
     }
 
     [Test]
@@ -40,7 +47,7 @@ public void GivenConcatMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = ConcatMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
@@ -48,7 +55,7 @@ public void GivenForEachMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = ForEachMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
@@ -56,7 +63,7 @@ public void GivenGroupByMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = GroupByMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
@@ -64,7 +71,7 @@ public void GivenToLookupMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = LookupMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
@@ -72,7 +79,7 @@ public void GivenUnionMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = UnionMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
@@ -80,30 +87,56 @@ public void GivenListsMethod_WhenDictionaryAB_ThenExpectedDictionary()
     {
         var mergedDictionary = UsingListsMethod(_dictionaryA, _dictionaryB);
 
-        CollectionAssert.AreEqual(_expectedMergedDictionary, mergedDictionary);
+        Assert.That(mergedDictionary, Is.EqualTo(_expectedMergedDictionary));
     }
 
     [Test]
-    public void GivenConcatMethod_WhenDictionariesWithDublicateKeys_ThenException()
+    public void GivenConcatMethod_WhenDictionariesWithDuplicateKeys_ThenException()
     {
         Assert.Throws<ArgumentException>(() => ConcatMethod(_dictionaryA, _dictionaryA));
     }
 
     [Test]
-    public void GivenUnionMethod_WhenDictionariesWithDublicateKeys_ThenException()
+    public void GivenUnionMethod_WhenDictionariesWithDuplicateKeys_ThenException()
+    {
+        Assert.Throws<ArgumentException>(() => UnionMethod(_dictionaryA, _clashingDictionary));
+    }
+
+    [Test]
+    public void GivenUnionMethod_WhenSameKeyWithSameValue_ThenNoException()
     {
-        Assert.Throws<ArgumentException>(() => UnionMethod(_dictionaryA, new Dictionary<int, string>()
-            {
-                {1, "Watermelon" } 
-                //key:1 already exists in _dictionaryA,
-                //but UnionMethod needs different key value pair to throw exception.
-            })
-        );
+        var mergedDictionary = UnionMethod(_dictionaryA, _dictionaryA);
+
+        Assert.That(mergedDictionary, Is.EqualTo(_dictionaryA));
     }
 
     [Test]
-    public void GivenListsMethod_WhenDictionariesWithDublicateKeys_ThenException()
+    public void GivenListsMethod_WhenDictionariesWithDuplicateKeys_ThenException()
     {
         Assert.Throws<ArgumentException>(() => UsingListsMethod(_dictionaryA, _dictionaryA));
     }
-}
\ No newline at end of file
+
+    [Test]
+    public void GivenForEachMethod_WhenDictionariesWithDuplicateKeys_ThenFirstValueKept()
+    {
+        var mergedDictionary = ForEachMethod(_dictionaryA, _clashingDictionary);
+
+        Assert.That(mergedDictionary[1], Is.EqualTo("Apple"));
+    }
+
+    [Test]
+    public void GivenGroupByMethod_WhenDictionariesWithDuplicateKeys_ThenFirstValueKept()
+    {
+        var mergedDictionary = GroupByMethod(_dictionaryA, _clashingDictionary);
+
+        Assert.That(mergedDictionary[1], Is.EqualTo("Apple"));
+    }
+
+    [Test]
+    public void GivenToLookupMethod_WhenDictionariesWithDuplicateKeys_ThenFirstValueKept()
+    {
+        var mergedDictionary = LookupMethod(_dictionaryA, _clashingDictionary);
+
+        Assert.That(mergedDictionary[1], Is.EqualTo("Apple"));
+    }
+}
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.csproj b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.csproj
index f02677bf64..dfb40caafc 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.csproj
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ConcatMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ConcatMethod.cs
index ef14f20038..e43f9b35ac 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ConcatMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ConcatMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> ConcatMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var mergedDictionary = dictionaries.Aggregate((dict1, dict2) =>
                     dict1.Concat(dict2).ToDictionary(kvp => kvp.Key, kvp => kvp.Value)
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ForEachMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ForEachMethod.cs
index 39a8275319..b0982146ff 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ForEachMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/ForEachMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> ForEachMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var mergedDictionary = new Dictionary<TKey, TValue>();
 
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/GroupByMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/GroupByMethod.cs
index 818adb08a7..3793684c97 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/GroupByMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/GroupByMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> GroupByMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var mergedDictionary = dictionaries.SelectMany(dict => dict)
                                                .GroupBy(kvp => kvp.Key)
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/LookupMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/LookupMethod.cs
index 11478a7285..e29489f35a 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/LookupMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/LookupMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> LookupMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var mergedDictionary = dictionaries.SelectMany(dict => dict)
                                                .ToLookup(pair => pair.Key, pair => pair.Value)
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UnionMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UnionMethod.cs
index 7807ec1051..9ece130e02 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UnionMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UnionMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> UnionMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var mergedDictionary = dictionaries.Aggregate((result, dict) =>
             {
diff --git a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UsingListsMethod.cs b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UsingListsMethod.cs
index 54ff653dbd..72d07521b4 100644
--- a/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UsingListsMethod.cs
+++ b/collections-csharp/MergingDictionariesInCSharp/MergingDictionariesInCSharp/Methods/UsingListsMethod.cs
@@ -3,6 +3,7 @@
     public partial class Methods
     {
         public static Dictionary<TKey, TValue> UsingListsMethod<TKey, TValue>(params Dictionary<TKey, TValue>[] dictionaries)
+            where TKey : notnull
         {
             var keys = new List<TKey>();
             var values = new List<TValue>();