title: No examples after join in Rapidminer
body: <p>Hi I am working on an assignment but I have a problem. 
  There are 2 datasets, the first has some flight information and the second has weather information. I want to predict whether a flight will depart with a delay of 15 minutes or more (using a decision tree). I have done the following: </p>
  
  <ul>
  <li>Import flight data -- select attributes -- split data -- parse numbers </li>
  </ul>
  
  <p>I selected the following attributes: day, dep_delay_15, dep_time_planned, dest_airport, dest_city, month, origin_airport, origin_city, origin_id and year. 
  After this I used split to split the dep_time_planned attribute into 2 parts (the first with the hour, the second with the minute) and I've parsed this. </p>
  
  <ul>
  <li>Import weather data -- select attributes</li>
  </ul>
  
  <p>Here I selected all of the attributes. 
  After this I have joined these datasets, but after the join all of the examples are gone (the attributes are still there). I have tried everything: left, right, inner and outer join. The key attribute couples I have made are:</p>
  
  <ul>
  <li>origin_id, airport_id</li>
  <li>day, day </li>
  <li>month, month </li>
  <li>dep_time_planned_1, hour </li>
  <li>year, year </li>
  </ul>
  
  <p>Can somebody help me out? </p>