@Override
	public byte[] getForwardModMapData(int oldVersion) throws IOException {
		if (bfMgr == null) {
			return null;
		}
		if (oldVersion < 1 || oldVersion >= version) {
			throw new IOException("Invalid mod-map version requested: " + oldVersion);
		}
		VersionFileHandler modMapGenerator =
			new VersionFileHandler(bfMgr, getFileId(), version, oldVersion);
		try {
			return modMapGenerator.getForwardModMapData();
		}
		finally {
			modMapGenerator.close();
		}
	}
Output old data for a specified buffer if required for version file.
@param index buffer index
@throws IOException
Ghidra/Framework/DB/src/main/java/db/buffers/LocalManagedBufferFile.java