public User userDTOToUser(AdminUserDTO userDTO) {
        if (userDTO == null) {
            return null;
        } else {
            User user = new User();
            user.setId(userDTO.getId());
            user.setLogin(userDTO.getLogin());
            user.setFirstName(userDTO.getFirstName());
            user.setLastName(userDTO.getLastName());
            user.setEmail(userDTO.getEmail());
            user.setImageUrl(userDTO.getImageUrl());
            user.setActivated(userDTO.isActivated());
            user.setLangKey(userDTO.getLangKey());
            Set<Authority> authorities = this.authoritiesFromStrings(userDTO.getAuthorities());
            user.setAuthorities(authorities);
            return user;
        }
    }
@Test
    void userDTOToUserMapWithNullAuthoritiesStringShouldReturnUserWithEmptyAuthorities() {
        userDto.setAuthorities(null);

        User user = userMapper.userDTOToUser(userDto);

        assertThat(user).isNotNull();
        assertThat(user.getAuthorities()).isNotNull();
        assertThat(user.getAuthorities()).isEmpty();
    }