It seems to be working but I need to ckeck again

src/intermediate_code.c

@@ -58,7 +58,16 @@ int S_Size(Stack *s){
     return s->size;
 }
 
-void S_Merge(Stack *s1, Stack *s2){
+void S_Merge(Stack *list){
+        Stack* s1 = S_Pop(list);
+        Stack* s2 = S_Peek(list);
+        if(s1 == NULL){
+                return;
+        }
+        if(s2 == NULL){
+                S_Push(list, s1, 0);
+                return;
+        }
         for (Instruction * i = S_Pop(s1); i; i = S_Pop(s1)){
                 S_Push(s2, i, 1);
         }