After removing the ROOT.war, the server behaves as if it exists (200 OK is returned and page is loaded empty) and the console shows the following NPE when browsing to a non existing path.
ERROR [CoyoteAdapter] An exception or error occurred in the container during the request processing
java.lang.NullPointerException
at org.apache.catalina.connector.CoyoteAdapter.parseSessionCookiesId(CoyoteAdapter.java:507)
at org.apache.catalina.connector.CoyoteAdapter.postParseRequest(CoyoteAdapter.java:449)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:239)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Thread.java:636)