Disabling QuickShare UI in Share causes exception

Regression: As per the instructions in https://issues.alfresco.com/jira/browse/ALF-16233 it should be possible to disable the quickshare UI action via share config. However, setting an empty url as per the example config results in a ftl exception which breaks Share.

To reproduce:
1) Add the following to share-config-custom.xml
<config evaluator="string-compare" condition="Social" replace="true">
<quickshare>
<url></url>
</quickshare>
</config>
2) Login to share

Result:
A blank page is displayed and this exception appears in the log:
Caused by: freemarker.core.InvalidReferenceException: The following has evaluated to null or missing:
==> config.scoped["Social"]["quickshare"].getChildValue("url") [in template "amd-modules/UrlConstants.get.js.ftl" at line 76, column 71]

Expected Result:
Login should be successful and the quickshare action should not be shown against documents.