What's wrong with that? For large systems, you'll never have a codebase that is 100% understood or 100% matches what the designers intended. If you want a robust, working, large system, you have to account for unintended things happening some of the time. In many cases, the right thing to do is to preserve or ignore nulls. Especially for client-side JavaScript (where clients are, by their nature, untrusted, and all authentication and data validation must happen on the server whether or not it also happens on the client), if some data fails to load due to a network blip, or the end-user does something unexpected and a div isn't initialized properly, or whatever, the right behavior for the software is to keep going, and the wrong behavior is to cause a minor error to turn into a major one.

In many other cases, of course, the robust thing to do is to catch a failure early and prevent some code from executing before it can do more harm, and err on the side of the system doing nothing instead of it doing something wrong. But neither of these is a universal rule.