fullstop-aws-support/fullstop-aws-cloudtrail-support/src/main/java/org/zalando/stups/fullstop/events/CloudTrailEventSupport.java
public static String getAccountId(final CloudTrailEvent event) {
        final CloudTrailEventData eventData = getEventData(event);
        final UserIdentity userIdentity = checkNotNull(eventData.getUserIdentity(), USER_IDENTITY_SHOULD_NEVER_BE_NULL);
        final String value = ofNullable(userIdentity.getAccountId()).orElse(eventData.getRecipientAccountId());
        return checkNotNull(value, ACCOUNT_ID_OR_RECIPIENT_SHOULD_NEVER_BE_NULL);
    }
public static String getAccountId(final CloudTrailEvent event) {
        final CloudTrailEventData eventData = getEventData(event);
        final UserIdentity userIdentity = checkNotNull(eventData.getUserIdentity(), USER_IDENTITY_SHOULD_NEVER_BE_NULL);
        final String value = ofNullable(userIdentity.getAccountId()).orElse(eventData.getRecipientAccountId());
        return checkNotNull(value, ACCOUNT_ID_OR_RECIPIENT_SHOULD_NEVER_BE_NULL);
    }
Extracts the 'accountId'.