mime type mapping for file names rather than suffixes removes first character of candidate file name before matching with key filename

public String getContentTypeFor(String fileName) {
        int idx = fileName.lastIndexOf('.');
        if (idx == -1) {
            idx = 0;
        }
        if (fileName.length() == idx) {
            return null;
        }
        String ext = fileName.substring(idx + 1); //BUG: when idx is zero we strip one character from the name
        return mMapping.get(ext);
    }