chore(draw): render connections without source

This allows us to renders temporary connections,
i.e. during create / connect.

lib/draw/BpmnRenderer.js

@@ -1327,21 +1327,26 @@ function BpmnRenderer(eventBus, styles, pathMap, canvas, priority) {
       var path = drawPath(parentGfx, pathData, attrs);
 
       var sequenceFlow = getSemantic(element);
-      var source = element.source.businessObject;
 
-      // conditional flow marker
-      if (sequenceFlow.conditionExpression && source.$instanceOf('bpmn:Activity')) {
-        svgAttr(path, {
-          markerStart: marker('conditional-flow-marker', fill, stroke)
-        });
-      }
+      var source;
 
-      // default marker
-      if (source.default && (source.$instanceOf('bpmn:Gateway') || source.$instanceOf('bpmn:Activity')) &&
-          source.default === sequenceFlow) {
-        svgAttr(path, {
-          markerStart: marker('conditional-default-flow-marker', fill, stroke)
-        });
+      if (element.source) {
+        source = element.source.businessObject;
+
+        // conditional flow marker
+        if (sequenceFlow.conditionExpression && source.$instanceOf('bpmn:Activity')) {
+          svgAttr(path, {
+            markerStart: marker('conditional-flow-marker', fill, stroke)
+          });
+        }
+
+        // default marker
+        if (source.default && (source.$instanceOf('bpmn:Gateway') || source.$instanceOf('bpmn:Activity')) &&
+            source.default === sequenceFlow) {
+          svgAttr(path, {
+            markerStart: marker('conditional-default-flow-marker', fill, stroke)
+          });
+        }
       }
 
       return path;

test/spec/draw/BpmnRendererSpec.js

@@ -2,8 +2,11 @@
 
 require('../../TestHelper');
 
+var svgCreate = require('tiny-svg/lib/create');
+
 var coreModule = require('../../../lib/core'),
-    rendererModule = require('../../../lib/draw');
+    rendererModule = require('../../../lib/draw'),
+    modelingModule = require('../../../lib/features/modeling');
 
 var domQuery = require('min-dom/lib/query');
 
@@ -249,6 +252,41 @@ describe('draw - bpmn renderer', function() {
   });
 
 
+  it('should render sequenceFlows without source', function(done) {
+
+    var xml = require('../../fixtures/bpmn/draw/colors.bpmn');
+    bootstrapModeler(xml, {
+      modules: [
+        coreModule,
+        rendererModule,
+        modelingModule
+      ]
+    })(function(err) {
+
+      inject(function(elementFactory, graphicsFactory) {
+
+        // given
+        var g = svgCreate('g');
+
+        var connection = elementFactory.create('connection', {
+          type: 'bpmn:SequenceFlow',
+          waypoints: [
+            { x: 0, y: 0 },
+            { x: 10, y: 100 }
+          ]
+        });
+
+        var gfx = graphicsFactory.drawConnection(g, connection);
+
+        expect(gfx).to.exist;
+      })();
+
+      done(err);
+    });
+
+  });
+
+
   describe('path', function() {
 
     var diagramXML = require('./BpmnRenderer.simple-cropping.bpmn');