What could generate memory leakage in this program

So I can't seem to find what does generate memory leakage in the next code.
My main looks like this

int main() {
    MovieRepo rep;
    _CrtDumpMemoryLeaks();
    return 0;
}

And MovieRepo class looks like this:

class MovieRepo{
protected:
    vector<Movie> all;
public:
    MovieRepo(){}
    ~MovieRepo(){}
}

And the Movie class looks like this:

class Movie {
    std::string title;
    std::string genre;
    std::string star;
    int year;

public:
    Movie(){}
    ~Movie(){}
}

The error I am getting from crtdbg:
Detected memory leaks!
Dumping objects ->
{152} normal block at 0x0094E710, 8 bytes long.
Data: < 9 > DC FB 39 00 00 00 00 00
Object dump complete.
Any idea?