CDDL is a File Based license. That is the CDDL applies to the individual files, not to everything within the project.
CDDL obligates you to release any CDDL files in your project, should you release a binary. Specifically, once a file is CDDL, any of your changes to that file automatically inherit that license and you are obligated to release your changes in that file along with the other CDDL files.
Any new files can be licensed however you want.
If you do "nothing" with your files, then you have implicit Copyright (at least in the U.S.), but haven't necessarily granted any rights to anyone else.
So, it's wise to either pick an actual license just to unmuddy the waters regarding your wishes on how you want the code used.
If you simply "don't care", you can put the code in the Public Domain, which waves your copyright (effectively, you lay NO claim to the work at all, no copyright, nothing, although no one else can copyright it either).
The CDDL is a good license, and out of simplicity and consistency, you can simply adopt that for your files.
Leaving it with just your implicit Copyright doesn't really let anyone do much of anything save read it. If you actually want your code to be potentially used, give it some license or a specific grant to the Public Domain. Its just a good courtesy today to be clear on such things.
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