When running Liferay with more than one node on a load balancer, sometimes, when generating urls for buttons, they can receive a incorrect url or sometimes a null value.
Resolution
Using the: redirect.url.security.mode=domain property in portal-ext.properties will fix this issue. redirect.url.security.mode=domain sets it so that Liferay portal will only redirect users to domains listed in the property redirect.url.domain.allowed.
The properties mentioned in the resolution are also discussed in: How to Set up Session Replication with Tomcat