code: private void addElement(String key, String value) {
          this.num_items++;
          List<String> vals = this.values.get(key);
          if (null == vals) {
              vals = new LinkedList<String>();
          }
          if (null == value) {
              vals.add("\"\"");
          } else {
              vals.add(value);
          }
          this.values.put(key, vals);
          if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled()) {
              Tr.debug(tc, "addElement: " + key + "=" + value + " num: " + this.num_items);
          }
      }
docs: Add the given key=value pair into storage. Both key and value must be
  in lowercase form. If this key already exists, then this value will be
  appended to the existing values.
  
  @param key
  @param value - if null then an empty string value is stored