Is using a MAC for encryption requiring a need for PKCS7 padding with this class?

I am working with this PHP encryption class using CRYPT_RIJNDAEL_256 and MCRYPT_MODE_CBC with a fixed 32-byte (64 character) HMAC key, as my basis.

The class is a result of previous discussions and remarks made on this blog page. and seems like a solid implementation as such. However there are a few aspects discussed I am still not clear on:

The only thing it adds is predictable plaintext positions which will aide a cryptanalyst. I recommend removing the serialization and using PKCS7 padding.

comment 1304.

Now that the encryption method uses HMAC and that the serialization avoids the '\0' padding issue. Is it still a good idea to use a PKCS padding even when the HMAC is used (and the serialization kept)?

Or in other words, does the HMAC alone solve the "predictable plaintext position"?