Use of RewriteHandler.LastRuleHandler without a child handler should produce a clear error message.

[joakime]

trafficstars

Jetty version(s) 12.0.13

Jetty Environment Any

Java version/vendor (use: java -version) Any

OS type/version Any

Description If an instance of a Handler.Wrapper without a child is allowed to start and begin handling requests, the error message is unclear.

java.lang.NullPointerException: Cannot invoke "org.eclipse.jetty.server.Request$Handler.handle(org.eclipse.jetty.server.Request, org.eclipse.jetty.server.Response, org.eclipse.jetty.util.Callback)" because "this._handler" is null

We should make the start of this kind of handler fail the start and throw a meaningful message that the Handler.Wrapper is missing a child.