How to send "empty" variable into JMeter
<p>I have some functional tests created via JMeter. It is pretty huge but i can't handle one simple check. 
I generate properties using BSF pre processor with help of JS. Parameter (lets call it "payment_fee") should be generated only if other parameter (lets call it "role") has a value = 1 .In this case we post pre generated integer into payment_fee and everything works well. But if role =2 then we should post nothing into payment_fee.
The problem is, i don't know how to say to JMeter: In case if role = 1 use variable with pre generated payment_fee but if role = 2, you shouldn't use this variable so just post an empty value for payment_fee  . Server waits for an integer so empty string or NULL had been rejected.</p>

<p>For more clarification:
I will try to explain more clear.
Here is a part of my code</p>

<pre><code>        var role = Math.floor(Math.random()*3+1)
        var paymentType = ["creditcard","cash"]
        var randomPay = installerType[Math.floor(Math.random()*installerType.length)];
        var payment = "";
        var paymentFee;
        if (role == 1){
            payment+=randomPay,
            paymentFee = Math.floor((Math.random() * 999) + 1) / 10.00
        }
vars.put("role", role);
vars.put("payment", payment);
vars.put("paymentFee", paymentFee);
</code></pre>

<p>And if role == 1 i should post paymentFee value. Like this - <a href="http://prntscr.com/b50kk1" rel="nofollow">http://prntscr.com/b50kk1</a> BUT! if role == 2 || role == 3 I should remove this value, so it should be like this <a href="http://prnt.sc/b50l82" rel="nofollow">http://prnt.sc/b50l82</a></p>