QueryParametersToHeadersMap implements UnaryOperator<Map<String, String>> { public static QueryParametersToHeadersMap getInstance(final HttpConfig httpConfig) { checkNotNull(httpConfig, "httpConfig"); return new QueryParametersToHeadersMap(httpConfig.getQueryParametersAsHeaders()); } private  QueryParametersToHeadersMap(final Set<HeaderDefinition> queryParametersAsHeaders); static QueryParametersToHeadersMap getInstance(final HttpConfig httpConfig); @Override Map<String, String> apply(final Map<String, String> queryParameters);  }
@Test public void tryToGetInstanceWithNullHttpConfig() { assertThatNullPointerException() .isThrownBy(() -> QueryParametersToHeadersMap.getInstance(null)) .withMessage("The httpConfig must not be null!") .withNoCause(); }