Object cannot be assigned to other types from DBNull

Question

I get minimum number in my database. But when no data in my database I get this error.

System.InvalidCastException: 'The object cannot be assigned to other types from DBNull.'

Code:

SqlCommand cmd = new SqlCommand("SELECT MAX(GidenEvrakSira) FROM GidenEvrak", con);    
SqlCommand smd = new SqlCommand("Select Min(GidenEvrakSira) FROM GidenEvrak Where UserID is null", con);    

con.Open();    

maxnum = Convert.ToInt32(cmd.ExecuteScalar());
minum = Convert.ToInt32(smd.ExecuteScalar());    

con.Close();

Answer 1

jdweng suggestion in comment is working:

var results = (cmd.ExecuteScalar() == DBNull.Value) ? null : cmd.ExecuteScalar();