code: public String[] getParameterValues(final String _key)
      {
          final Map<String, String[]> params = getParameters();
          return params != null ? params.get(_key) : null;
      }
docs: Evaluates with given key in the list of all parameters for given key and
  returns them (if found) as string array. If not found a <code>null</code>
  is returned.
  
  @param _key name of parameter values which should returned
  @return array of parameter values for given key of <code>null</code> if
  not exists
  @see #getParameters to get the map of parameters