Simplify `update()` logic in `MovieService` and `TvShowService`

[dvt32]

Currently we have something like:

                        if (movieDetails.getTitle() != null) {
                existingMovie.setTitle(movieDetails.getTitle());
            }
            if (movieDetails.getDescription() != null) {
                existingMovie.setDescription(movieDetails.getDescription());
            }
            if (movieDetails.getRating() != null) {
                existingMovie.setRating(movieDetails.getRating());
            }
            if (movieDetails.getReleaseDate() != null) {
                existingMovie.setReleaseDate(movieDetails.getReleaseDate());
            }
            if (movieDetails.getDirector() != null) {
                existingMovie.setDirector(movieDetails.getDirector());
            }
            if (movieDetails.getWriter() != null) {
                existingMovie.setWriter(movieDetails.getWriter());
            }
            if (movieDetails.getStars() != null) {
                existingMovie.setStars(movieDetails.getStars());
            }
            if (movieDetails.getDuration() != null) {
                existingMovie.setDuration(movieDetails.getDuration());
            }
            if (movieDetails.getImdbId() != null) {
                existingMovie.setImdbId(movieDetails.getImdbId());
            }
            if (movieDetails.getYear() != null) {
                existingMovie.setYear(movieDetails.getYear());
            }

Find a way to refactor and simplify the method, so that it's easier to maintain if we introduce more fields for movies and TV shows.

[ali-al-fntext]

It took for a while but done :)