RuntimeException is recorded in the logs when adding a web link after Webhook creation

Steps to reproduce

1. install new JIRA 6.1.5
2. add a new project and create new issue
3. add a new Webhook as per NewWebhook.png
4. add a link using the Web Link as per Weblink.png
5. issue is linked correctly, but JIRA throws this error in the log:

   2014-01-22 18:11:10,437 http-bio-9615-exec-17 ERROR admin 1091x690x1 1e7mb5x 127.0.0.1 /secure/AddWebLink.jspa [atlassian.event.internal.AsynchronousAbleEventDispatcher] There was an exception thrown trying to dispatch event 'com.atlassian.jira.event.issue.link.RemoteIssueLinkCreateEvent@3c7ab8c3' from the invoker 'SingleParameterMethodListenerInvoker{method=public void com.atlassian.webhooks.plugin.WebHookEventsProcessor.onEvent(java.lang.Object), listener=com.atlassian.webhooks.plugin.WebHookEventsProcessor@59ab4398}'.
   java.lang.RuntimeException: com/atlassian/plugins/rest/common/json/JacksonJsonProviderFactory
   	at com.atlassian.event.internal.SingleParameterMethodListenerInvoker.invoke(SingleParameterMethodListenerInvoker.java:54)
   	at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$2.run(AsynchronousAbleEventDispatcher.java:66)
   	at com.atlassian.event.internal.AsynchronousAbleEventDispatcher$1.execute(AsynchronousAbleEventDispatcher.java:32)
   	at com.atlassian.event.internal.AsynchronousAbleEventDispatcher.dispatch(AsynchronousAbleEventDispatcher.java:60)
   	at com.atlassian.event.internal.EventPublisherImpl.invokeListeners(EventPublisherImpl.java:160)
   	at com.atlassian.event.internal.EventPublisherImpl.publish(EventPublisherImpl.java:79)
   	at com.atlassian.jira.issue.link.DefaultRemoteIssueLinkManager.createRemoteIssueLink(DefaultRemoteIssueLinkManager.java:113)
   	at com.atlassian.jira.bc.issue.link.DefaultRemoteIssueLinkService.create(DefaultRemoteIssueLinkService.java:280)
   	at com.atlassian.jira.bc.issue.link.DefaultRemoteIssueLinkService.create(DefaultRemoteIssueLinkService.java:254)
   ...
   Caused by: java.lang.NoClassDefFoundError: com/atlassian/plugins/rest/common/json/JacksonJsonProviderFactory
   	at com.atlassian.linkaggregation.jira.webhooks.RemoteIssueLinkEventSerializerFactory$1.getWebHookBody(RemoteIssueLinkEventSerializerFactory.java:37)
   	at com.atlassian.webhooks.plugin.OsgiWebHookProviderWebHookRegistry$2$1.get(OsgiWebHookProviderWebHookRegistry.java:90)
   	at com.atlassian.webhooks.plugin.OsgiWebHookProviderWebHookRegistry$2$1.get(OsgiWebHookProviderWebHookRegistry.java:86)
   

Notes

• This is tested with JIRA 6.1.5
• Events such as Created, Updated seems to be posted correctly to requestb.in