Make filter fields optional and update README

Author: Brian Earwood

README.md

@@ -58,8 +58,8 @@ The following is a complete list of options available for configuration in [engi
 | `titleField`       | String        | optional          | The field to display as the title in results.                                                                                                                                          |
 | `urlField`         | String        | optional          | A field with a url to use as a link in results.                                                                                                                                        |
 | `urlFieldTemplate` | String        | optional          | Instead of urlField, you can provide a URL "template" here, which lets you build a URL from other fields. ex: "https://www.example.com/{{id}}".                                        |
-| `sortFields`       | Array[String] | required          | A list of fields that will be used for sort options.                                                                                                                                   |
-| `facets`           | Array[String] | required          | A list of fields that will be available as "facet" filters. Read more about facets within the [App Search documentation](https://swiftype.com/documentation/search-lib/guides/facets). |
+| `sortFields`       | Array[String] | optional          | A list of fields that will be used for sort options.                                                                                                                                   |
+| `facets`           | Array[String] | optional          | A list of fields that will be available as "facet" filters. Read more about facets within the [App Search documentation](https://swiftype.com/documentation/search-lib/guides/facets). |
 
 ### External configuration
 

src/search-lib/SearchDriver.js

@@ -297,12 +297,18 @@ export default class SearchDriver {
         current,
         size: resultsPerPage
       },
-      facets: removeConditionalFacets(this.facetConfig, filters),
       filters: {
         all: formatORFiltersAsAND(convertRangeFiltersToDateString(filters))
       }
     };
 
+    const facets = removeConditionalFacets(this.facetConfig, filters);
+    const numberOfFacets = Object.keys(facets).length;
+
+    if (numberOfFacets > 0) {
+      searchOptions.facets = facets;
+    }
+
     if (sortField && sortDirection) {
       searchOptions.sort = {
         [sortField]: sortDirection