describe() fails on union databanks

What steps will reproduce the problem?
1. using jquery.rdfquery.rules-1.0.js
2. Here is my test code that demonstrates the problem:

        console.log("This will test a problem with databank.describe on a union databank");

        var t1 = "<http://example.org/#ex1> a <http://example.org/#Example>";
        var t2 = "<http://example.org/#ex2> a <http://example.org/#Example>";
        var subjects = '';
        var graph1 = $.rdf().add(t1);
        graph1.where('?s a ?o').each(function(i) { subjects += this.s.toString()});
        console.log("graph1 subjects: "+subjects);
        subjects = '';

        var graph2 = $.rdf().add(t2);
        graph2.where('?s a ?o').each(function(i) { subjects += this.s.toString()});
        console.log("graph2 subjects: "+subjects);
        subjects = '';

        // graph3 will be a union graph
        var graph3 = $.rdf().add(graph1).add(graph2);
        var g3subjects = '';
        graph3.where('?s a ?o').each(function(i) { g3subjects += this.s.toString()});
        console.log("graph3 subjects: "+g3subjects);

        console.log("graph3.describe will FAIL with the rdfquery 1.0");
        graph3.where('?s a ?o').describe(['?s']).forEach(function(v,i,a) { console.log(v.toString())});        

Instead of triples I get: 
[TypeError: Cannot read property '<http://example.org/#ex1>' of undefined]

I apologize that I can't give a proper patch because I've made a few minor 
changes around the lib to make it node.js compatible, however, I fixed my 
working version by modifying the databank.describe() function like this:

    describe: function (resources) {
      var i, r, t, rhash = {}, triples = [];
      while (resources.length > 0) {
        r = resources.pop();
        if (rhash[r] === undefined) {
          if (r.value === undefined) {
            r = $.rdf.resource(r);
          }
          if (this.union !== undefined) {
            this.union.forEach(function(v,i,a){
              eachDatabank.call(v);
            });
          }
          else {
            eachDatabank.call(this);
          }
          function eachDatabank() {
            if (this.tripleStore[r] !== undefined) {
              for (i = 0; i < this.tripleStore[r].length; i += 1) {
                t = this.tripleStore[r][i];
                triples.push(t);
                if (t.object.type === 'bnode') {
                  resources.push(t.object);
                }
              }
            }
            if (this.objectStore[r] !== undefined) {
              for (i = 0; i < this.objectStore[r].length; i += 1) {
                t = this.objectStore[r][i];
                triples.push(t);
                if (t.subject.type === 'bnode') {
                  resources.push(t.subject);
                }
              }
            }
          };
          rhash[r] = true;
        }
      }
      return $.unique(triples);
    },
Original issue reported on code.google.com by anderson...@gmail.com on 6 Jan 2012 at 9:39
nasar2016 / rdfquery

describe() fails on union databanks #36
