Refactor conjunction.cpp to handle null cost in compute_cost method

src/conjunction.cpp

@@ -1,11 +1,18 @@
 #include "conjunction.hpp"
 #include "statement.hpp"
+#include "core.hpp"
 
 namespace riddle
 {
     conjunction::conjunction(scope &parent, std::shared_ptr<env> ctx, const conjunction_statement &conj) : scope(parent.get_core(), parent), ctx(ctx), conj(conj) {}
 
     void conjunction::execute() { conj.execute(*this, ctx); }
 
-    std::shared_ptr<arith_item> conjunction::compute_cost() const noexcept { return std::static_pointer_cast<arith_item>(conj.get_cost()->evaluate(*this, ctx)); }
+    std::shared_ptr<arith_item> conjunction::compute_cost() const noexcept
+    {
+        if (conj.get_cost())
+            return std::static_pointer_cast<arith_item>(conj.get_cost()->evaluate(*this, ctx));
+        else
+            return get_core().new_real(utils::rational::one);
+    }
 } // namespace riddle