C# .NET - how to remove the empty line when reading the text file

hi, i want to remove the empty line when reading the text file. if it has empty line means my project is not working. i used the following code to read the text file
                StreamReader readtxtfile = new StreamReader(filename);
                string str = null;
                List<string> str1 = new List<string>();
                while ((str = readtxtfile.ReadLine()) != null)
                 {
                    str1.Add(Convert.ToString(str));
                }
i tried .Trim(), but its not working for me.

try to modified your code with below.. see the bold highlighted portion i have added

 StreamReader readtxtfile = new StreamReader(filename);
                string str = null;
                List<string> str1 = new List<string>();
                while ((str = readtxtfile.ReadLine()) != null)
                 {
            // if line is empty or blank then it will not insert into your List <string>
            if (! String.IsNullOrEmpty(str))
            {
                str1.Add(Convert.ToString(str));
              }
          }