Problem with adding row to table using C#

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C#

SQL

server

hello all.
I'm using C#.NET(2013) and SQL Server(2014).
What's this code's error?

SqlConnection conn = new SqlConnection("database=myDB;data source=(local); integrated security=true");
conn.Open();
SqlDataAdapter da = new SqlDataAdapter("select * from Book", conn);
DataSet ds = new DataSet();
da.Fill(ds, "Book");
DataTable dt = ds.Tables["Book"];

DataRow dr = dt.NewRow();

dr["bookName"] = "C#.NET";
dr["bookISBN"] = "FW-593"; //Primary Key
dr["bookPrice"] = "15000";
dr["bookPubDate"] = "1392/1/9";

dt.Rows.Add(dt);
SqlCommandBuilder cb = new SqlCommandBuilder(da);
da.Update(ds,"book");

Error:
Cannot insert the value NULL into column 'bookISBN', table 'myDB.dbo.Book'; column does not allow nulls. INSERT fails.