Ensure docUrlRoot is defined with a fallback to an empty string

Author: ksuess

docs/_static/searchtools.js

@@ -114,7 +114,7 @@ function _getBreadcrumbs(item, linkUrl) {
 
 const _displayItem = (item, searchTerms) => {
   const docBuilder = DOCUMENTATION_OPTIONS.BUILDER;
-  const docUrlRoot = DOCUMENTATION_OPTIONS.URL_ROOT;
+  const docUrlRoot = DOCUMENTATION_OPTIONS.URL_ROOT || "";
   const docFileSuffix = DOCUMENTATION_OPTIONS.FILE_SUFFIX;
   const docLinkSuffix = DOCUMENTATION_OPTIONS.LINK_SUFFIX;
   const showSearchSummary = DOCUMENTATION_OPTIONS.SHOW_SEARCH_SUMMARY;