Fix issue with Identity nb output.

include/aidge/operator/Identity.hpp

@@ -40,7 +40,7 @@ public:
     static const std::string Type;
 
     Identity_Op()
-            : OperatorTensor(Type, 1, 0, 0)
+            : OperatorTensor(Type, 1, 0, 1)
     {
         mImpl = std::make_shared<OperatorImpl>(*this);
     }
@@ -101,7 +101,10 @@ public:
         if (outputIdx >= nbInputs()) {
             AIDGE_THROW_OR_ABORT(std::runtime_error, "%s Operator has %hu outputs", type().c_str(), nbInputs());
         }
-        return mInputs[outputIdx];
+        if (mInputs[outputIdx] == nullptr){
+            return mOutputs[outputIdx]; // Input is not initialized with empty tensor
+        }
+        return mInputs[outputIdx]; // Identity, so Output is Input
     }
     void setBackend(const std::string& /*name*/, DeviceIdx_t /*device*/ = 0) override final {
         // setBackend do nothing, Identity node has no backend it just pass the same Tensor