The gluon.site module request that the structure elements are called to get
the actual content of the string. The simple-uci will not do that and
instead cause an exception because the caller didn't provide a string.

closes #19

Siehe https://github.com/freifunk-gluon/gluon/commit/7ccdacd294e5fcb6718f806543bb2620c02c9ddb