handlingnull.java

String constructionFirm = person.getResidence().getAddress().getConstructionFirm();
//Can't do this because residence, address or constructionFirm could be null.

String constructionFirm = null;
if(person != null){
   Residence residence = person.getResidence();
   if(residence != null){
      Address address = residence.getAddress();
      if(address != null){
         constructionFirm = adress.getConstructionFirm();
      }
   }
}