title: NIFI || Send Mail only for True boolean expression
body: <p>I am calculating value using below expression:
  ${alert:gt(${Lower}):or(${alert:lt(${UPPER})})} which in turn is returning either True or false value.</p>
  <p>As per requirement I have to send a mail notification for True condition only.
  can someone tell me suitable condition to send only true condition from above calculation.</p>
  <p><a href="https://i.stack.imgur.com/E1fIL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E1fIL.png" alt="enter image description here" /></a></p>