What happens if you call the delete operator on nullptr?

Nothing will happen. Calling the delete operator on nullptr does not lead to an error or undefined behavior. The C++ standard explicitly guarantees this.

int* p = nullptr;
delete p; // Safe, nothing happens.

int* q = new int(10);
delete q; // Frees the allocated memory.
delete q; // Undefined behavior (double delete).

int* r = new int[5];
delete[] r; // Frees the array.