default Stream<? extends PrimaryKeyColumn> primaryKeyColumns() {
        return table()
            .map(Table::primaryKeyColumns)
            .orElse(Stream.empty())
            .filter(HasEnabled::test);
    }
Returns a stream over all enabled primary key columns in the node tree.
Disabled nodes will be ignored.

@return the enabled primary key columns
@see PrimaryKeyColumn
@see HasEnabled#isEnabled()
generator-parent/generator-translator/src/main/java/com/speedment/generator/translator/Translator.java