How do I print out error message if I enter an input that doesn't exist in Database? N-Tier

Question

A quick brief explanation on my question: I want to my program to print out an error message without crashing the program if I enter a number that doesn't exist in my program's Database. Here is my code:

  listBox1.Items.Clear();

  BusinessTier.Business BT = new BusinessTier.Business("netflix.mdf");

  if (this.txtMovieID == null) //Hoping this would work and return to the program if I enter a wrong input. 
  {
    listBox1.Items.Add("**Error, this movie ID doesn't exist, or database is empty?!");
  }

  int N = System.Convert.ToInt32(this.txtMovieID.Text);
  BusinessTier.Movie movie = BT.GetMovie(N);

  BusinessTier.MovieDetail movieid = BT.GetMovieDetail(movie.MovieID); //this part will crash the program if I type a number like 0 or greater than 250 when my database contained 250 rows. 


  //display results:

  listBox1.Items.Add(movie.MovieName);

  foreach (BusinessTier.Review r in movieid.Reviews)
  {
    listBox1.Items.Add(r.UserID + ": " + r.Rating);
  }

Answer 1

First thing : you are still processing the remaining part of the process, i.e retrieving the Movie Details, even if this.txtMovieID is null. You need to stop the processing and return

  listBox1.Items.Clear();

  BusinessTier.Business BT = new BusinessTier.Business("netflix.mdf");

  if (this.txtMovieID == null) //Hoping this would work and return to the program if I enter a wrong input. 
  {
    listBox1.Items.Add("**Error, this movie ID doesn't exist, or database is empty?!");
    return; // exit out if the MovieID is null
  }

Second : put a check to see whether the result of GetMovie(N) is null or not and if it is null, break and return

  int N = System.Convert.ToInt32(this.txtMovieID.Text);
  BusinessTier.Movie movie = BT.GetMovie(N);

  if (movie == null) return; // exit if the GetMovie result is null

  BusinessTier.MovieDetail movieid = BT.GetMovieDetail(movie.MovieID); //this part will crash the program if I type a number like 0 or greater than 250 when my database contained 250 rows. 

  //display results:

  listBox1.Items.Add(movie.MovieName);

  foreach (BusinessTier.Review r in movieid.Reviews)
  {
      listBox1.Items.Add(r.UserID + ": " + r.Rating);
  }