diff --git a/src/Exceptions/MappingFail.php b/src/Exceptions/MappingFail.php
index 2c58885..6e35b30 100644
--- a/src/Exceptions/MappingFail.php
+++ b/src/Exceptions/MappingFail.php
@@ -8,15 +8,18 @@ class MappingFail extends DTOException
 {
     public function __construct(
         public readonly Mapper $mapper,
-        public readonly UnexpectedValue|InternalException|null $exception = null
+        public readonly UnexpectedValue|InternalException|string|null $exception = null
     ) {
         parent::__construct(
             sprintf(
                 '[%s]%s',
                 $mapper::class,
-                $exception ? " {$exception->getMessage()}" : ''
+                is_string($exception)
+                    ? $this->exception
+                    : ($exception ? " {$exception->getMessage()}" : '')
+
             ),
-            previous: $exception
+            previous: ! is_string($exception) ? $exception : null
         );
     }
 }
diff --git a/src/Support/Mapping/Casts/KeyedArrayCast.php b/src/Support/Mapping/Casts/KeyedArrayCast.php
index c568f7b..26d8747 100644
--- a/src/Support/Mapping/Casts/KeyedArrayCast.php
+++ b/src/Support/Mapping/Casts/KeyedArrayCast.php
@@ -29,7 +29,7 @@ class KeyedArrayCast extends OptionalCast
      */
     protected array|OneOfConstCast|EnumCast|StringCast|null $keyBy = null;
 
-    protected bool $nullIfEmpty = false;
+    protected bool $optionalIfEmpty = false;
 
     protected bool $stdClassCastAllowed = false;
 
@@ -75,13 +75,22 @@ public function keySchema(OneOfConstCast|EnumCast|StringCast $cast): static
 
     public function nullIfEmpty(): static
     {
-        $this->nullIfEmpty = true;
+        $this->optionalIfEmpty = true;
 
         $this->nullable();
 
         return $this;
     }
 
+    public function optionalIfEmpty(): static
+    {
+        $this->optionalIfEmpty = true;
+
+        $this->optional();
+
+        return $this;
+    }
+
     protected function finalize(mixed $source, array $sourcesTrace): ?stdClass
     {
         $value = static::resolveValueFromAccessor(
@@ -145,7 +154,7 @@ protected function finalize(mixed $source, array $sourcesTrace): ?stdClass
             }
         }
 
-        return ! $hasValues && $this->nullIfEmpty ? null : $result;
+        return ! $hasValues && $this->optionalIfEmpty ? null : $result;
     }
 
     protected function types(): RecordType