java-Match a regex pattern in a string(listing matching and non-matching parts)

i have a csv string containing five fields(3 mandatory and 2 optional). The optional fields are in posiition 3 and 5. I have a regex pattern to identify the strings in double quotes

    private static final String TEXT_IN_DBL_QUOTES_REGEX="\"([^\"]*)\"";
    private static final String rowData="\"Field1\", \"Field2\", , \"Field4\", ";

    public static void main(String[] args){
        List<String> fields = Lists.newArrayList();
        Pattern regex = Pattern.compile(TEXT_IN_DBL_QUOTES_REGEX);
        Matcher matcher = regex.matcher(rowData);
        while(matcher.find()){
           fields.add(matcher.group(1));
        }
        return fields;
    }

My expected result is an array list containing 
Field1, Field2, null, Field4, null
but the above is returning 
Field1, Field2, Field4

How can i tweak the above code to get the desired result?