StoredProcOutboundGateway produces NPE in case of null from the DB and expect-single-result="true"

If payload = resultMap.values().iterator().next(); returns null, the next this.getMessageBuilderFactory().withPayload(payload).copyHeaders(requestMessage.getHeaders()).build() ends up with the java.lang.IllegalArgumentException: payload must not be null.

As a workaround do not extract single result and get deal with the whole Map downstream manually.
Therefore it isn't critical and may be backported to 4.2.x and below on demand.