public T getValueOrThrow() throws ParseException {
        String text = getText();

        T parseResult = parser.parse(text);

        if ("".equals(text)) {
            return null;
        }

        return parseResult;
    }
Return the parsed value, or null if the field is empty.

@throws ParseException if the value cannot be parsed
stroom-core-client-widget/src/main/java/com/google/gwt/user/client/ui/ValueBoxBase.java