Refactor

Make signature of What.RunAsync `void` and remove async
modifier. Subsequently, move down the call stack and
make everything that needed to be async to support
this being async synchronous.

Enable Nullable and fix potential null references.

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();
     }
 }

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>

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));
         }

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()));
         }
     }
 }