@Override
public int compare(BaseModelObject oObj1, BaseModelObject oObj2) {
Document oDoc1 = oObj1.getDocument();
Document oDoc2 = oObj2.getDocument();
DataType oTyp = oDoc1.attribute(sAtr).type().getDataType();
Comparable oAtr1=null, oAtr2=null;
switch (oTyp) {
case STRING:
if (oDoc1.attribute(sAtr).isEmpty())
oAtr1 = null;