Incomplete C++ solution for Clone Graph passes test suite

[s-kunwar]

Bug Report for https://neetcode.io/problems/clone-graph

Submitting an incomplete C++ solution that only contains a nullptr check for the empty graph case gets marked as Accepted and passes all 18 test cases.

Here's the code to reproduce the bug:

class Solution {
public:
    Node* cloneGraph(Node* node) {
        if (node == nullptr) return nullptr;
    }
};

The submission should fail with a Wrong Answer, Segmentation Fault, or Runtime Error when evaluated against non-empty graph inputs. But the judge marks the submission as Accepted.