I have create WCF service. I am trying to use DotNetNuke.Data.DataProvider.Instance() but it throws exception System.NullReferenceException. The code as follows:

WCF service code:

public List<DialogInfo> GetDisease(int DialogId, bool IsDisplayed)
{
return DialogController.GetDialog(DialogId, IsDisplayed);
}

Controller code:

public static class DialogController
{
public static List<DialogInfo> GetDialog(int DialogId, bool IsDisplayed)
{
return CBO.FillCollection<DialogInfo>(DotNetNuke.Data.DataProvider.Instance().ExecuteReader("GetDialog", DialogId, IsDisplayed));
}
}

Please help me to findout if I am missing any reference.