code: @Nullable
    public static String getQueryParametersAsString (@Nullable final List <? extends URLParameter> aQueryParams,
                                                     @Nullable final IEncoder <String, String> aQueryParameterEncoder)
    {
      if (CollectionHelper.isEmpty (aQueryParams))
        return null;
  
      final StringBuilder aSB = new StringBuilder ();
      // add all values
      for (final URLParameter aParam : aQueryParams)
      {
        // Separator
        if (aSB.length () > 0)
          aSB.append (AMPERSAND);
        aParam.appendTo (aSB, aQueryParameterEncoder);
      }
  
      return aSB.toString ();
    }
docs: Create a parameter string. This is also suitable for POST body (e.g. for
  web form submission).
  
  @param aQueryParams
  Parameter map. May be <code>null</code> or empty.
  @param aQueryParameterEncoder
  The encoder to be used to encode parameter names and parameter
  values. May be <code>null</code>. This may be e.g. a
  {@link URLParameterEncoder}.
  @return <code>null</code> if no parameter is present.