ReferenceGenome constructor fixed to accept null arg

frontend-js/src/main/js/map/data/ReferenceGenome.js

@@ -3,7 +3,7 @@
 var ReferenceGenomeGeneMapping = require('./ReferenceGenomeGeneMapping');
 
 function ReferenceGenome(javaObject) {
-  if (javaObject !== undefined) {
+  if (javaObject !== undefined && javaObject !== null) {
     this.setType(javaObject.type);
     this.setVersion(javaObject.version);
     if (javaObject.localUrl !== undefined) {

frontend-js/src/test/js/map/data/ReferenceGenome-test.js

@@ -32,4 +32,10 @@ describe('ReferenceGenome', function() {
     var genome = new ReferenceGenome();
     assert.ok(genome);
   });
+
+  it("contructor with null arg", function() {
+    var genome = new ReferenceGenome(null);
+    assert.ok(genome);
+  });
+
 });