without this change we created a "fallback span" in the case where a Spring component didn't handle the span. By handling it means that it got processed by anyway (a tag, log was added etc.). Why did we do that? That's because if no component was involved in creation of additional spans then in the Zipkin UI the service that had only the span that has the SR, SS logs wouldn't show up. In other words, if service A called service B and service B had only a single span, then service B wouldn't show up in the UI (there would be no blue bar). All the data would show up however in the client side of that span.
with this change we're removing this behaviour. That's because it introduces confusion for our users, that use non Spring related components. Also it seems that the Zipkin UI got fixed and this error no longer is present. If however it turns out that it's still there, it clearly seems that the place to fix this error should be Zipkin and not Sleuth.
fixes#708
1b1a1698ca