fix(import): gracefully handle missing waypoints

This ensures we do not blow up if a diagram
is missing waypoints for connections.

Related to camunda/camunda-modeler#1294

lib/import/BpmnImporter.js

@@ -1,6 +1,5 @@
 import {
-  assign,
-  map
+  assign
 } from 'min-dash';
 
 import { is } from '../util/ModelUtil';
@@ -31,8 +30,15 @@ function elementData(semantic, attrs) {
   }, attrs);
 }
 
-function collectWaypoints(waypoints) {
-  return map(waypoints, function(p) {
+function getWaypoints(bo, source, target) {
+
+  var waypoints = bo.di.waypoint;
+
+  if (!waypoints || waypoints.length < 2) {
+    return [ getMid(source), getMid(target) ];
+  }
+
+  return waypoints.map(function(p) {
     return { x: p.x, y: p.y };
   });
 }
@@ -151,7 +157,7 @@ BpmnImporter.prototype.add = function(semantic, parentElement) {
       hidden: hidden,
       source: source,
       target: target,
-      waypoints: collectWaypoints(semantic.di.waypoint)
+      waypoints: getWaypoints(semantic, source, target)
     }));
 
     if (is(semantic, 'bpmn:DataAssociation')) {

test/spec/import/ImporterSpec.js

@@ -418,6 +418,21 @@ describe('import - Importer', function() {
     });
 
 
+    it('should import sequence flow without waypoints', function(done) {
+
+      // given
+      var xml = require('./sequenceFlow-missingWaypoints.bpmn');
+
+      // when
+      runImport(diagram, xml, function(err, warnings) {
+
+        expect(warnings).to.be.empty;
+
+        done(err);
+      });
+    });
+
+
     it('should extend attributes with default value', function(done) {
 
       // given

test/spec/import/sequenceFlow-missingWaypoints.bpmn

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<definitions xmlns="http://www.omg.org/spec/BPMN/20100524/MODEL" xmlns:bpmndi="http://www.omg.org/spec/BPMN/20100524/DI" xmlns:omgdi="http://www.omg.org/spec/DD/20100524/DI" xmlns:omgdc="http://www.omg.org/spec/DD/20100524/DC" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" id="sid-38422fae-e03e-43a3-bef4-bd33b32041b2" targetNamespace="http://bpmn.io/bpmn" exporter="bpmn-js (https://demo.bpmn.io)" exporterVersion="3.2.1">
+  <process id="Process_1" isExecutable="false">
+    <startEvent id="Event">
+      <outgoing>SequenceFlow</outgoing>
+    </startEvent>
+    <task id="Task">
+      <incoming>SequenceFlow</incoming>
+    </task>
+    <sequenceFlow id="SequenceFlow" sourceRef="Event" targetRef="Task" />
+  </process>
+  <bpmndi:BPMNDiagram id="BpmnDiagram_1">
+    <bpmndi:BPMNPlane id="BpmnPlane_1" bpmnElement="Process_1">
+      <bpmndi:BPMNShape id="Event_di" bpmnElement="Event">
+        <omgdc:Bounds x="163" y="151" width="36" height="36" />
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNShape id="Task_di" bpmnElement="Task">
+        <omgdc:Bounds x="249" y="129" width="100" height="80" />
+      </bpmndi:BPMNShape>
+      <bpmndi:BPMNEdge id="SequenceFlow_di" bpmnElement="SequenceFlow">
+      </bpmndi:BPMNEdge>
+    </bpmndi:BPMNPlane>
+  </bpmndi:BPMNDiagram>
+</definitions>