public void save() throws IOException {
        if (!grammars.isEmpty()) {
            log.debug("Persisting grammars dependency status: " + statusFile);

            ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(
                        statusFile));

            try {
                out.writeObject(grammars);
            } finally {
                out.close();
            }
        }
    }
Determines the package to use.

@param   arguments  the tool arguments.

@return  the package. Returns {@code null} to indicate that no package should be
         used.
antlr4-maven-plugin/src/main/java/org/antlr/mojo/antlr4/GrammarDependencies.java