feat: allow command and query validation rules to return null

In this instance, null indicates no errors.

CHANGELOG.md

@@ -5,6 +5,10 @@ All notable changes to this project will be documented in this file. This projec
 
 ## Unreleased
 
+### Added
+
+- The command and query validators now allow rules to return `null` to indicate no errors.
+
 ### Changed
 
 - BREAKING: changed the `ErrorIterableInterface` to `ListOfErrorsInterface`. Result objects now only accept list of

src/Bus/Validation/AbstractValidator.php

@@ -19,6 +19,7 @@
 
 namespace CloudCreativity\Modules\Bus\Validation;
 
+use CloudCreativity\Modules\Bus\Results\ListOfErrors;
 use CloudCreativity\Modules\Bus\Results\ListOfErrorsInterface;
 use CloudCreativity\Modules\Toolkit\Pipeline\AccumulationProcessor;
 use CloudCreativity\Modules\Toolkit\Pipeline\PipeContainerInterface;
@@ -77,8 +78,10 @@ protected function getPipeline(): PipelineInterface
     private function processor(): AccumulationProcessor
     {
         return new AccumulationProcessor(
-            static fn (?ListOfErrorsInterface $carry, ListOfErrorsInterface $errors): ListOfErrorsInterface =>
-                $carry ? $carry->merge($errors) : $errors,
+            static function (?ListOfErrorsInterface $carry, ?ListOfErrorsInterface $errors): ListOfErrorsInterface {
+                $errors ??= new ListOfErrors();
+                return $carry ? $carry->merge($errors) : $errors;
+            },
         );
     }
 }

tests/Unit/Bus/Validation/CommandValidatorTest.php

@@ -43,14 +43,19 @@ public function test(): void
             return new ListOfErrors($error1);
         };
 
-        $b = function ($actual) use ($command, $error2, $error3): ListOfErrors {
+        $b = function ($actual) use ($command): ?ListOfErrors {
+            $this->assertSame($command, $actual);
+            return null;
+        };
+
+        $c = function ($actual) use ($command, $error2, $error3): ListOfErrors {
             $this->assertSame($command, $actual);
             return new ListOfErrors($error2, $error3);
         };
 
         $validator = new CommandValidator(new PipelineBuilderFactory());
         $actual = $validator
-            ->using([$a, $b])
+            ->using([$a, $b, $c])
             ->validate($command);
 
         $this->assertInstanceOf(ListOfErrors::class, $actual);

tests/Unit/Bus/Validation/QueryValidatorTest.php

@@ -43,14 +43,19 @@ public function test(): void
             return new ListOfErrors($error1);
         };
 
-        $b = function ($actual) use ($query, $error2, $error3): ListOfErrors {
+        $b = function ($actual) use ($query): ?ListOfErrors {
+            $this->assertSame($query, $actual);
+            return null;
+        };
+
+        $c = function ($actual) use ($query, $error2, $error3): ListOfErrors {
             $this->assertSame($query, $actual);
             return new ListOfErrors($error2, $error3);
         };
 
         $validator = new QueryValidator(new PipelineBuilderFactory());
         $actual = $validator
-            ->using([$a, $b])
+            ->using([$a, $b, $c])
             ->validate($query);
 
         $this->assertInstanceOf(ListOfErrors::class, $actual);