@Override
    public String toString() {
        return new StringJoiner(", ", NullDelegatingMapper.class.getSimpleName() + "[", "]")
            .add("index=" + index)
            .add("delegate=" + delegate)
            .toString();
    }
Delegating mapper that implements the &#0064;PropagateNull semantics to check a specific column in the result set for null first. If that column is null,
return null as the value, otherwise executed the delegated mapper.

@param <T> The generic type for the row mapper.
core/src/main/java/org/jdbi/v3/core/mapper/reflect/internal/NullDelegatingMapper.java