Neo4j lowest node java procedure -

i creating procedure return lowest node in database have problem. code not work me. compile using maven after start crash. code here:

@context public graphdatabaseservice db; @procedure @description("return lowest node") public stream<stringresult> get() {     resourceiterable<string> low = db.getallpropertykeys();     list<string> node = new arraylist<string>();     while(low.iterator().hasnext()){         string next = low.iterator().next();         node.add(next);     }     string = collections.min(node);     return stream.of(new stringresult(collections.min(node)));     }  public class stringresult { public final string value;  public stringresult(string value) {     this.value = value; } 

}

i thankfull if u me because confused.