Improve command signature logic

src/Command.php

@@ -53,13 +53,13 @@ class Command
             } else {
                 $type = $parameter->getType();
                 if ($type instanceof ReflectionNamedType && $type->isBuiltin()) {
-                    $type = $type->getName();
+                    $type = ($type->allowsNull() ? "?" : "") . $type->getName();
                 } else {
                     $type = null;
                 }
             }
             
-            if ($parameter->isOptional()) $type = "?{$type}";
+            if ($parameter->isDefaultValueAvailable()) $type = "{$type}=".\json_encode($parameter->getDefaultValue(),\JSON_UNESCAPED_SLASHES);
             if ($type !== null) $args[$name] = $type;
         }