code: @Nullable
    @OverrideOnDemand
    protected String getQueryString (@Nonnull final LECTYPE aLEC)
    {
      return aLEC.params ().getAsString (PARAM_QUERY);
    }
docs: Get the provided query string from the parameter map. By default the value
  of parameter {@link #PARAM_QUERY} is used.
  
  @param aLEC
  The layout execution context.
  @return <code>null</code> if no such request parameter is present.