passing file name to a method; how do you create null values in a SQL server database via a C# program

Question

1.I've created code that reads in a text file from a particular format and creates a SQL server database.  I would like to encapsulate this code in a method.  I would like to pass a file name into this method as a parameter which would be used to define a stream reader object file dynamically:

StreamReader tr = File.OpenText("C://My Documents//filename.txt");

Does anyone know how to do this?

2.  In created variables from my text files, some of the values are missing which I would like to convert to null values in SQL SERVER.  How can I do this?

Thanks