private void exit(int exitCode) {
        if (exitCode != 0) {
            LOG.error("exiting: {}", exitCode);
        } else {
            LOG.info("exiting: {}", exitCode);
        }
        System.exit(exitCode);
    }
returns stack trace if there was a container exception or empty string
if there was no stacktrace

@param t
@param metadataList
@return
tika-core/src/main/java/org/apache/tika/pipes/PipesServer.java