diff --git a/CliFx.Tests/HelpTextSpecs.cs b/CliFx.Tests/HelpTextSpecs.cs
index 7e5304d..9359ec8 100644
--- a/CliFx.Tests/HelpTextSpecs.cs
+++ b/CliFx.Tests/HelpTextSpecs.cs
@@ -223,56 +223,6 @@ public class NamedChildCommand : ICommand
         stdErr.Should().NotBeNullOrWhiteSpace();
     }
 
-    // Regression test for #117
-    [Fact]
-    public async Task Help_text_lists_parameters_in_specified_order()
-    {
-        // Arrange
-        var commandType = DynamicCommandBuilder.Compile(
-            // language=cs
-            @"
-public abstract class CommandBase : ICommand
-{
-    [CommandParameter(0)]
-    public string Foo { get; set; }
-
-    public abstract ValueTask ExecuteAsync(IConsole console);
-}
-
-[Command]
-public class Command : CommandBase
-{
-    [CommandParameter(1)]
-    public string Bar { get; set; }
-    
-    [CommandParameter(2)]
-    public IReadOnlyList<string> Baz { get; set; }
-    
-    public override ValueTask ExecuteAsync(IConsole console) => default;
-}
-");
-
-        var application = new CliApplicationBuilder()
-            .AddCommand(commandType)
-            .UseConsole(FakeConsole)
-            .Build();
-
-        // Act
-        var exitCode = await application.RunAsync(
-            new[] { "--help" },
-            new Dictionary<string, string>()
-        );
-
-        var stdOut = FakeConsole.ReadOutputString();
-
-        // Assert
-        exitCode.Should().Be(0);
-        stdOut.Should().ContainAllInOrder(
-            "USAGE",
-            "<foo>", "<bar>", "<baz...>"
-        );
-    }
-
     [Fact]
     public async Task Help_text_shows_application_metadata()
     {
@@ -421,6 +371,57 @@ public class Command : ICommand
         );
     }
 
+    // https://github.com/Tyrrrz/CliFx/issues/117
+    [Fact]
+    public async Task Help_text_shows_usage_format_which_lists_all_parameters_in_specified_order()
+    {
+        // Arrange
+        var commandType = DynamicCommandBuilder.Compile(
+            // language=cs
+            @"
+// Base members appear last in reflection order
+public abstract class CommandBase : ICommand
+{
+    [CommandParameter(0)]
+    public string Foo { get; set; }
+
+    public abstract ValueTask ExecuteAsync(IConsole console);
+}
+
+[Command]
+public class Command : CommandBase
+{
+    [CommandParameter(2)]
+    public IReadOnlyList<string> Baz { get; set; }
+
+    [CommandParameter(1)]
+    public string Bar { get; set; }
+    
+    public override ValueTask ExecuteAsync(IConsole console) => default;
+}
+");
+
+        var application = new CliApplicationBuilder()
+            .AddCommand(commandType)
+            .UseConsole(FakeConsole)
+            .Build();
+
+        // Act
+        var exitCode = await application.RunAsync(
+            new[] { "--help" },
+            new Dictionary<string, string>()
+        );
+
+        var stdOut = FakeConsole.ReadOutputString();
+
+        // Assert
+        exitCode.Should().Be(0);
+        stdOut.Should().ContainAllInOrder(
+            "USAGE",
+            "<foo>", "<bar>", "<baz...>"
+        );
+    }
+
     [Fact]
     public async Task Help_text_shows_usage_format_which_lists_all_required_options()
     {
diff --git a/CliFx/Extensibility/BindingValidator.cs b/CliFx/Extensibility/BindingValidator.cs
index 08897a7..92a5e2c 100644
--- a/CliFx/Extensibility/BindingValidator.cs
+++ b/CliFx/Extensibility/BindingValidator.cs
@@ -29,7 +29,7 @@ public abstract class BindingValidator<T> : IBindingValidator
     /// You can use the utility methods <see cref="Ok"/> and <see cref="Error"/> to
     /// create an appropriate result.
     /// </remarks>
-    public abstract BindingValidationError? Validate(T value);
+    public abstract BindingValidationError? Validate(T? value);
 
-    BindingValidationError? IBindingValidator.Validate(object? value) => Validate((T) value!);
+    BindingValidationError? IBindingValidator.Validate(object? value) => Validate((T?) value);
 }
\ No newline at end of file
diff --git a/CliFx/Formatting/HelpConsoleFormatter.cs b/CliFx/Formatting/HelpConsoleFormatter.cs
index 97483dc..5e10e0d 100644
--- a/CliFx/Formatting/HelpConsoleFormatter.cs
+++ b/CliFx/Formatting/HelpConsoleFormatter.cs
@@ -72,7 +72,7 @@ internal class HelpConsoleFormatter : ConsoleFormatter
             Write(' ');
 
             // Parameters
-            foreach (var parameter in _context.CommandSchema.Parameters)
+            foreach (var parameter in _context.CommandSchema.Parameters.OrderBy(p => p.Order))
             {
                 Write(ConsoleColor.DarkCyan, parameter.Property.IsScalar()
                     ? $"<{parameter.Name}>"
diff --git a/CliFx/Schema/ApplicationSchema.cs b/CliFx/Schema/ApplicationSchema.cs
index 445f840..308515e 100644
--- a/CliFx/Schema/ApplicationSchema.cs
+++ b/CliFx/Schema/ApplicationSchema.cs
@@ -16,8 +16,8 @@ internal partial class ApplicationSchema
 
     public IReadOnlyList<string> GetCommandNames() => Commands
         .Select(c => c.Name)
-        .Where(n => !string.IsNullOrWhiteSpace(n))
-        .ToArray()!;
+        .WhereNotNullOrWhiteSpace()
+        .ToArray();
 
     public CommandSchema? TryFindDefaultCommand() =>
         Commands.FirstOrDefault(c => c.IsDefault);
diff --git a/CliFx/Schema/CommandSchema.cs b/CliFx/Schema/CommandSchema.cs
index d71687e..cc75f7d 100644
--- a/CliFx/Schema/CommandSchema.cs
+++ b/CliFx/Schema/CommandSchema.cs
@@ -89,13 +89,12 @@ internal partial class CommandSchema
 
         var parameterSchemas = type.GetProperties()
             .Select(ParameterSchema.TryResolve)
-            .Where(p => p is not null)
-            .OrderBy(p => p!.Order)
+            .WhereNotNull()
             .ToArray();
 
         var optionSchemas = type.GetProperties()
             .Select(OptionSchema.TryResolve)
-            .Where(o => o is not null)
+            .WhereNotNull()
             .Concat(implicitOptionSchemas)
             .ToArray();
 
@@ -103,8 +102,8 @@ internal partial class CommandSchema
             type,
             name,
             description,
-            parameterSchemas!,
-            optionSchemas!
+            parameterSchemas,
+            optionSchemas
         );
     }
 
diff --git a/CliFx/Utils/Extensions/CollectionExtensions.cs b/CliFx/Utils/Extensions/CollectionExtensions.cs
index a2d7375..23dfcf1 100644
--- a/CliFx/Utils/Extensions/CollectionExtensions.cs
+++ b/CliFx/Utils/Extensions/CollectionExtensions.cs
@@ -6,6 +6,25 @@ namespace CliFx.Utils.Extensions;
 
 internal static class CollectionExtensions
 {
+    public static IEnumerable<T> WhereNotNull<T>(this IEnumerable<T?> source)
+        where T : class
+    {
+        foreach (var i in source)
+        {
+            if (i is not null)
+                yield return i;
+        }
+    }
+
+    public static IEnumerable<string> WhereNotNullOrWhiteSpace(this IEnumerable<string?> source)
+    {
+        foreach (var i in source)
+        {
+            if (!string.IsNullOrWhiteSpace(i))
+                yield return i;
+        }
+    }
+
     public static void RemoveRange<T>(this ICollection<T> source, IEnumerable<T> items)
     {
         foreach (var item in items)
@@ -17,5 +36,5 @@ internal static class CollectionExtensions
         IEqualityComparer<TKey> comparer) =>
         dictionary
             .Cast<DictionaryEntry>()
-            .ToDictionary(entry => (TKey) entry.Key, entry => (TValue) entry.Value, comparer)!;
+            .ToDictionary(entry => (TKey) entry.Key, entry => (TValue) entry.Value, comparer);
 }
\ No newline at end of file