[C#][Windows Forms] How to stop passing value from one form to other in formclosing event? : So, I got 2 forms (form1,form2),**form1** is the main form. I got one textbox and one radiobutton and a simple button in form2, and 1 onlyreadable-textbox with label on the side, and simple button in **form1**. The form1 button opens the form2 window. In form2, I can write numbers in textbox, and then select the valute on radio button(Euro) and when I click on the passvalue button the numbers and valute are passed to the form 1 textbox(numbers) and label(valute). That works fine, but when I open the form2 window and don't write anything in textbox, also don't check the radiobutt, and click on the red X for closing the form 2, the form will close and the values in form 1(where there was added values before) disappears. For example: I add a value of 2000 euros to form 1 textbox&label, and then when I open one more time the form2, and leave the texbox clear and radiobutt unchecked, close the form2 with the X, the form1 values of 2000 euros will disappear.
Here's the source code of the passing values and buttons:

        FORM2
        private string pss;
        public string Passvalue
        {  
                      
            get { return pss; }
            set { pss = value; }
        }
        private string pss2;  
        public string Passvalue2
        {
            get { return pss2; }
            set { pss2 = value; }
        }
    public void Btn1_Click(object sender, EventArgs e)//The passvalue button
        {
            string eur="EUR";
            Passvalue = ukupnaCifraTB.Text;//textbox form2=the number sender
            ukupnaCifraTB.Text = String.Empty;
           
            
           
            if (radioButton1.Checked)
            {
                radioButton1.Text = eur;
                Passvalue2 = radioButton2.Text;
            }

            this.Close();

        }
Here's form1:

    private string backvalue;
        public string BackedValue
        {
            get { return backvalue; }
            set { backvalue = value; }           
        }

        private string backedText;
        public string BackedText
        {
            get { return backedText; }
            set { backedText =  value; }
        }
       public void Btn1_Click(object sender, EventArgs e)
        {
            Form2 f2 = new Form2(); 
            f2.ShowDialog();
            trenutnoStanjeTB.Text = f2.Passvalue;//trenutnostanjeTB=textbox(form1)=gets number from form2
            DinEuLab1.Text = f2.Passvalue2;//dineulab1=label form1=gets the eur text
            DinEuLab2.Text = f2.Passvalue2;

        }

 What I need to change/add to resolve my problem? **I want that when I once pass the values, and then open the form2 and close it, to not send the empty values to form1.**


 