private void emitContentsAndBytes(Emitter emitter, EmitKey emitKey,
                                      MetadataListAndEmbeddedBytes parseData) {
        if (!(emitter instanceof StreamEmitter)) {
            throw new IllegalArgumentException("The emitter for embedded document byte store must" +
                    " be a StreamEmitter. I see: " + emitter.getClass());
        }
        //TODO: implement this
        throw new UnsupportedOperationException("this is not yet implemented");
    }
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