Optional generated for element having default value

[Dries]

We encountered a case where an Optional was generated for a default value.

Given the following XMLSchema:

<xsd:element name="volgnummer" type="algemeen:Volgnummer" minOccurs="0" default="1"/>

resulted in following Java code which does not compile:

    public Optional<Integer> getVolgnummer() {
        if (null == volgnummer) {
            return new Integer(1);
        }
        return volgnummer;
    }

(note: we als have a generator for default values)

It turns out the current check for default values is not sufficient. I'll provide a PR for it.