Fix ConstantFolding bug

src/recipes/ConstantFolding.cpp

@@ -36,6 +36,7 @@ void Aidge::constantFolding(std::shared_ptr<GraphView> graph) {
         for (const auto& node : candidates) {
             bool foldable = true;
             auto replaceGraph = std::make_shared<GraphView>();
+            size_t i = 0;
             for (const auto& input : node->inputs()) {
                 if (input.first) {
                     if (input.first->type() != Producer_Op::Type) {
@@ -53,6 +54,13 @@ void Aidge::constantFolding(std::shared_ptr<GraphView> graph) {
 
                     replaceGraph->add(input.first, false);
                 }
+                else if (node->inputCategory(i) != InputCategory::OptionalData
+                    && node->inputCategory(i) != InputCategory::OptionalParam)
+                {
+                    foldable = false;
+                    break;
+                }
+                ++i;
             }
 
             if (foldable) {