title: Preprocessor variables are not available on websocket request
body: <p>I'm adding a variable on a BeanShell Preprocessor:
  vars.put("var",value).
  I use it on a WebSocket request:
  ${var}.
  When I send the request, the request body contains '${var}' instead of the value itself.</p>
  
  <p>I tried to use also JSR223 Preprocessor.
  I tried to put on the request '${_V(value)' and put it as property but nothing is working</p>