(#555) Clarify ITypeResolver returns null

and does not throw on unresolvable types.
Also changed the TypeResolverAdapter to adhere
to those expectations and removed the now no longer
needed try-catch from CommandPropertyBinder.

examples/Cli/Injection/Infrastructure/TypeResolver.cs

@@ -15,7 +15,12 @@ namespace Spectre.Console.Examples
 
         public object Resolve(Type type)
         {
-            return _provider.GetRequiredService(type);
+            if (type == null)
+            {
+                return null;
+            }
+
+            return _provider.GetService(type);
         }
 
         public void Dispose()

src/Spectre.Console/Cli/ITypeResolver.cs

@@ -11,7 +11,7 @@ namespace Spectre.Console.Cli
         /// Resolves an instance of the specified type.
         /// </summary>
         /// <param name="type">The type to resolve.</param>
-        /// <returns>An instance of the specified type.</returns>
+        /// <returns>An instance of the specified type, or <c>null</c> if no registration for the specified type exists.</returns>
         object? Resolve(Type? type);
     }
 }

src/Spectre.Console/Cli/Internal/Binding/CommandPropertyBinder.cs

@@ -27,18 +27,11 @@ namespace Spectre.Console.Cli
         }
 
         private static CommandSettings CreateSettings(ITypeResolver resolver, Type settingsType)
-        {
-            try
         {
             if (resolver.Resolve(settingsType) is CommandSettings settings)
             {
                 return settings;
             }
-            }
-            catch
-            {
-                // ignored
-            }
 
             if (Activator.CreateInstance(settingsType) is CommandSettings instance)
             {

src/Spectre.Console/Cli/Internal/TypeResolverAdapter.cs

@@ -20,14 +20,9 @@ namespace Spectre.Console.Cli
 
             try
             {
-                if (_resolver != null)
+                var obj = _resolver?.Resolve(type);
+                if (obj != null)
                 {
-                    var obj = _resolver.Resolve(type);
-                    if (obj == null)
-                    {
-                        throw CommandRuntimeException.CouldNotResolveType(type);
-                    }
-
                     return obj;
                 }