title: runtimeservice.getVariables does not work because it can't find process instance id
body: <p>I'm new to flowable and I'm trying to start a process instance with variables. <code>params</code> here is the Map of <code>&lt;String,Object&gt;</code> that I'm using to start the process. It all goes well, but if I try to get my variables back it tells me </p>
  
  <pre><code>"execution 22f42f67-5f88-11e9-9df0-d46d6dbfea92 doesn't exist"
  </code></pre>
  
  <p>But if I search for it in my process instances list, is there. This is what I do:</p>
  
  <pre><code>pi = runtimeService.startProcessInstanceById(processDefinitionId, params);
  runtimeService.getVariables(pi.getId());
  </code></pre>
  
  <p>I'm stuck with this problem and I do not understand why it keeps doing this. What am I missing?</p>