object reference not set to an instance of an object. in c#

Question

next line is in connection.cs file= 

public OleDbDataReader dr;

 

 

 

and this is in form.cs file 

oleDbCommand.Connection = connection.Conn;

connection.dr = oleDbCommand.ExecuteReader();

 

i got exception = 

object reference not set to an instance of an object. in c#