diff --git a/Contracts/What.cs b/Contracts/What.cs
index 8c683a3..f8c6088 100644
--- a/Contracts/What.cs
+++ b/Contracts/What.cs
@@ -1,11 +1,9 @@
-using System.Threading.Tasks;
-
-namespace DotWhat.Contracts
+namespace DotWhat.Contracts
 {
     public abstract class What
     {
         public abstract string Name { get; }
 
-        public abstract Task RunAsync();
+        public abstract void Run();
     }
-}
\ No newline at end of file
+}
diff --git a/DotWhat.csproj b/DotWhat.csproj
index 7acb83e..f6c64dd 100644
--- a/DotWhat.csproj
+++ b/DotWhat.csproj
@@ -1,12 +1,14 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
     <TargetFramework>net5.0</TargetFramework>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Cocona.Lite" Version="1.5.0" />
+    <PackageReference Include="Roslynator.Analyzers" Version="3.0.0" PrivateAssets="all" />
   </ItemGroup>
 
 </Project>
diff --git a/DuckTyping/CustomAwaiters.cs b/DuckTyping/CustomAwaiters.cs
index 05a5be7..5222daa 100644
--- a/DuckTyping/CustomAwaiters.cs
+++ b/DuckTyping/CustomAwaiters.cs
@@ -1,7 +1,6 @@
 using DotWhat.Contracts;
 using System;
 using System.Runtime.CompilerServices;
-using System.Threading.Tasks;
 
 namespace DotWhat.DuckTyping
 {
@@ -9,9 +8,9 @@ namespace DotWhat.DuckTyping
     {
         public override string Name => "CustomAwaiters";
 
-        public override async Task RunAsync()
+        public override async void Run()
         {
-            int i = 123;
+            const int i = 123;
 
             Console.WriteLine(await (await await 7 + await i));
         }
@@ -35,4 +34,4 @@ namespace DotWhat.DuckTyping
         {
         }
     }
-}
\ No newline at end of file
+}
diff --git a/Program.cs b/Program.cs
index 82a32ce..9c0eb96 100644
--- a/Program.cs
+++ b/Program.cs
@@ -1,29 +1,29 @@
-using DotWhat.Contracts;
+using Cocona;
+using DotWhat.Contracts;
 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
 using System.Threading.Tasks;
-using Cocona;
 
 namespace DotWhat
 {
-    class Program
+    internal class Program
     {
-        private static readonly IEnumerable<What> Whats =
+        private static readonly IEnumerable<What?> Whats =
             Assembly.GetExecutingAssembly()
                 .GetTypes()
                 .Where(type => type.BaseType == typeof(What))
-                .Select(what => (What)Activator.CreateInstance(what));
+                .Select(what => (What?)Activator.CreateInstance(what));
 
         private static async Task<int> Main(string[] args)
         {
-            await CoconaLiteApp.RunAsync<Program>(args);
+            await CoconaLiteApp.RunAsync<Program>(args).ConfigureAwait(false);
 
             return 0;
         }
 
-        public async Task StartAsync([Argument] string name = default)
+        public void Start([Argument] string? name = default)
         {
             if (string.IsNullOrEmpty(name))
             {
@@ -32,7 +32,7 @@ namespace DotWhat
                 return;
             }
 
-            var command = Whats.FirstOrDefault(what => what.Name.Equals(name, StringComparison.OrdinalIgnoreCase));
+            var command = Whats.FirstOrDefault(what => what!.Name.Equals(name, StringComparison.OrdinalIgnoreCase));
 
             if (command is null)
             {
@@ -41,10 +41,10 @@ namespace DotWhat
                 return;
             }
 
-            await command.RunAsync();
+            command.Run();
 
             static void PrintWhats()
-                => Whats.ToList().ForEach(what => Console.WriteLine(what.Name.ToLower()));
+                => Whats.ToList().ForEach(what => Console.WriteLine(what!.Name.ToLower()));
         }
     }
-}
\ No newline at end of file
+}