code: public String getAsQueryString(Object key) {
          StringBuilder sb = new StringBuilder();
          key = OAuth.percentEncode((String) key);
          Set<String> values = wrappedMap.get(key);
          if (values == null) {
              return key + "=";
          }
          Iterator<String> iter = values.iterator();
          while (iter.hasNext()) {
              sb.append(key + "=" + iter.next());
              if (iter.hasNext()) {
                  sb.append("&");
              }
          }
          return sb.toString();
      }
docs: Concatenates all values for the given key to a list of key/value pairs
  suitable for use in a URL query string.
  
  @param key
  the parameter name
  @return the query string