* Also updates the facetFieldSet for O(1) lookup performance.
     *
     * @param facetFields array of field names that can be used for faceted search
     */
    public void setFacetFields(final String[] facetFields) {
        this.facetFields = facetFields;
        facetFieldSet = new HashSet<>();
        Collections.addAll(facetFieldSet, facetFields);
    }

    /**

        queryFieldConfig.setFacetFields(fields);

        String[] result = queryFieldConfig.getFacetFields();
        assertSame(fields, result);
    }

    @Test
    public void test_setFacetFields() {
        String[] fields = { "facet1", "facet2", "facet3" };
        queryFieldConfig.setFacetFields(fields);

        assertSame(fields, queryFieldConfig.facetFields);

     * Test that setting facet fields creates both array and Set.
     */
    @Test
    public void test_setFacetFields_createsSet() {
        String[] fields = { "facet1", "facet2", "facet3" };
        queryFieldConfig.setFacetFields(fields);

        // Verify array is set
        assertNotNull(queryFieldConfig.facetFields);
        assertSame(fields, queryFieldConfig.facetFields);
        assertEquals(3, queryFieldConfig.facetFields.length);