Although many static-analysis techniques have been developed for automatically detecting bugs, such as null dereferences, fewer automated approaches have been presented for analyzing whether and how such bugs are fixed. Attempted bug fixes may be incomplete in that a related manifestation of the bug remains unfixed. In this paper, we characterize the “completeness” of attempted bug fixes that involve the flow of invalid values from one program point to another, such as null dereferences, in Java programs. Our characterization is based on the definition of a bug neighborhood, which is a scope of flows of invalid values. We present an automated analysis that, given two versions P and P' of a program, identifies the bugs in P that have been fixed in P', and classifies each fix as complete or incomplete. We implemented our technique for null-dereference bugs and conducted empirical studies using open-source projects. Our results indicate that, for the projects we studied, many bug fixes are not complete, and thus, may cause failures in subsequent executions of the program.