When `len` is a positive int, and the queried key has empty value, `string::resize(-1)` will be called, and an exception occurs. A purposed fix is [here](https://github.com/concretevitamin/succinct-cpp/commit/0e4564967f5338bab24d7540d6ad11057a3de0be).
When
lenis a positive int, and the queried key has empty value,string::resize(-1)will be called, and an exception occurs.A purposed fix is here.