Fix the case where qWhere[idKey] is null

lib/scope.js

@@ -130,7 +130,13 @@ ScopeDefinition.prototype.related = function(receiver, scopeParams, condOrRefres
           return mergedWhere;
         };
         if (queryRelated.where !== undefined) {
+          if (!queryRelated.where[IdKey]) {
+            // If it's null, don't bother calling smartMerge or model.find.
+            // Simply return an empty result to the client.
+            return cb(null, []);
+          } else {
             queryRelated.where = buildWhere();
+          }
         } else {
           queryRelated.where = {};
           queryRelated.where[IdKey] = collectTargetIds(data, IdKey);

test/relations.test.js

@@ -819,6 +819,15 @@ describe('relations', function() {
             done();
           });
         });
+        it('returns empty result when filtering with wrong id key', function(done) {
+          var wrongWhereFilter = {where: {wrongIdKey: samplePatientId}};
+          physician.patients(wrongWhereFilter, function(err, ch) {
+            if (err) return done(err);
+            should.exist(ch);
+            ch.should.have.lengthOf(0);
+            done();
+          });
+        });
         it('returns patients where id in an array', function(done) {
           var idArr = [];
           var whereFilter;