https://github.com/SpiderLabs/secrules-language-tests/blob/c8cf2c588a93dce20781e597643e1b9d11aa4bba/transformations/cssDecode.json#L24-L28
The linked test case appears to be broken to me. After checking this and the actual code I'm fairly certain that the two spaces after the last null byte should be preserved sice the null byte is not a hexadecimal escape.
