private void handleOOM(String taskId, OutOfMemoryError oom) {
        write(STATUS.OOM);
        LOG.error("oom: " + taskId, oom);
        exit(1);
    }
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