public static Boolean asNullableBoolean(final String str) {
        if (str == null) {
            return null;
        } else {
            return asBoolean(str);
        }
    }
@return Null if str is null. True if str is equal to one of (y|yes|true|on|enabled|1)
ignoring case, else false.
stroom-util/src/main/java/stroom/util/string/StringUtil.java