private byte[] getForwardModMapData() throws IOException {
		if (bfMgr == null) {
			return null;
		}
		File mf = bfMgr.getChangeMapFile();
		if (mf == null || !mf.exists()) {
			return null;
		}
		ChangeMapFile modMap = new ChangeMapFile(mf, this);
		try {
			return modMap.getModData();
		}
		finally {
			modMap.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