/**
  * Gets the input-only expression mappings.
  *
  * @return the input-only expression mappings
  */
 public List<ExpressionMapping> getInputOnlyExpressionMappings() {
   List<ExpressionMapping> list = new LinkedList<ExpressionMapping>();
   for (ExpressionMapping em : _inputExpressionMappings) {
     if (em.getOutput() == null) {
       list.add(em);
     }
   }
   return list;
 }
 /**
  * Gets the input-output expression mappings.
  *
  * @return the input-output expression mappings
  */
 public Map<String, ExpressionMapping> getInputOutputExpressionMappings() {
   Map<String, ExpressionMapping> map = new LinkedHashMap<String, ExpressionMapping>();
   for (ExpressionMapping em : _inputExpressionMappings) {
     String output = em.getOutput();
     if (output != null) {
       if (map.containsKey(output)) {
         throw new IllegalArgumentException(
             "duplicate input/output variable [" + output + "] not allowed");
       } else {
         map.put(output, em);
       }
     }
   }
   return map;
 }