The execution context for the prepare/send message step is empty (except for the wiki ID)

When a message is being prepared (in the background thread) from the prepare queue a new execution context (and XWikiContext) is created in order for each message to be prepared in isolation from one another, however this step might need information from the execution context when the sendAsynchronously call was made.

For example, in preparing a message (like rendering a message template), you might need the current user. Right now the current user is guest (null reference) since the context is new and only the wiki ID is set in the XWikiContext.