diff --git a/src/Libs/Synapsis.php b/src/Libs/Synapsis.php
index 8ffcf21..96035b2 100644
--- a/src/Libs/Synapsis.php
+++ b/src/Libs/Synapsis.php
@@ -118,7 +118,7 @@ class Synapsis
             $reflectionClass = new ReflectionClass($className);
             $constructor = $reflectionClass->getConstructor();
             static::$instances[$className] = new $className(
-                ...static::resolveParameterValues($constructor->getParameters())
+                ...static::resolveParameterValues($constructor?->getParameters() ?? [])
             );
         }
 
@@ -141,13 +141,17 @@ class Synapsis
                 continue;
             }
 
-            // Intentamos darle un valor equivalente a nulo si es una clase primitiva pare evitar
-            // errores innecesarios, lo
-            if ($parameter->getType()->isBuiltin()) {
-                throw new Exception('Primitive parameters expect at least a default value.');
+            $paramType = $parameter->getType();
+            if ($paramType === null) {
+                // If no type is declared, and it's not optional, we cannot resolve it.
+                throw new Exception('Untyped parameters expect at least a default value or must be optional.');
             }
 
-            $values[] = static::resolveInstance($parameter->getType()->getName());
+            if ($paramType->isBuiltin()) {
+                throw new Exception("Primitive parameter '{$parameter->getName()}' expects at least a default value.");
+            }
+
+            $values[] = static::resolveInstance($paramType->getName());
         }
         return $values;
     }