gistfile1.java

final String[] input = new String[] {"dave", "john",
                null, "dan", null, "matt"};
final String resultSkip = Joiner.on(",")
        .skipNulls()
        .join(input);

// resultSkip = "dave,john,dan,matt"

final String resultUseForNull = Joiner.on(",")
        .useForNull("<blank>")
        .join(input);

// resultUseForNull = "dave,john,<blank>,dan,<blank>,matt"