private DateFormat determineDateFormat() {
        return dfStr == null ? null : new SimpleDateFormat(dfStr, Locale.getDefault());
    }
TODO replace method call with reflection in tests.

@param dateFormat dateFormat
@deprecated This method will break internal state of the instance by setting formatter which is not using
format provided using constructor. It will be removed in future releases.
core/src/main/java/com/github/dozermapper/core/converters/DateFormatContainer.java