InfoPath Dev

I have the following code that populates 3 fields on my infopath form from the querystring:

public void InternalStartup()
        {
           EventManager.FormEvents.Loading += new LoadingEventHandler(FormEvents_Loading);
        }

public void FormEvents_Loading(object sender, LoadingEventArgs e)
        {
            string Partner = string.Empty;
            string Lawyer = string.Empty;
            string PartnerEmail = string.Empty;
            try
            {
                e.InputParameters.TryGetValue("Partner", out Partner);
                e.InputParameters.TryGetValue("Lawyer", out Lawyer);
                e.InputParameters.TryGetValue("PartnerEmail", out PartnerEmail);
            }
            catch (Exception ex)
            {
                Partner = ex.Message.ToString();
                Lawyer = ex.Message.ToString();
                PartnerEmail = ex.Message.ToString();
            }
            finally
            {
                MainDataSource.CreateNavigator().SelectSingleNode("//my:PartnerResponsible", NamespaceManager).SetValue(Partner);
                MainDataSource.CreateNavigator().SelectSingleNode("//my:LawyerDealing", NamespaceManager).SetValue(Lawyer);
                MainDataSource.CreateNavigator().SelectSingleNode("//my:PartnerEmail", NamespaceManager).SetValue(PartnerEmail);
            }
        }

At the moment I get an error when opening an already populated form as the querysrting values are only supplied to the form if it is a brand new form. How can I stop this running if the form is already populated or the querysting parameters does not exist.

Thanks

Jeni

 Sorted!

Wonderful - mind posting your solution for others? Are you checking the InputParameters for the key? (e.InputParameters.ContainsKey)

 I just put and if statement around the finally part:

 finally
            {

                if (Partner!=null)

                {

                MainDataSource.CreateNavigator().SelectSingleNode("//my:PartnerResponsible", NamespaceManager).SetValue(Partner);
                MainDataSource.CreateNavigator().SelectSingleNode("//my:LawyerDealing", NamespaceManager).SetValue(Lawyer);
                MainDataSource.CreateNavigator().SelectSingleNode("//my:PartnerEmail", NamespaceManager).SetValue(PartnerEmail);

                }
            }